Who Shouldn't Get Credit Cards?
Credit cards are obviously a problem if you're racking up credit card debt, but less obviously a problem if you're not carrying a balance but are spending more than you would otherwise if using debit cards. Credit cards should be treated as a privilege for those who are making otherwise wise financial decisions like insurance, savings, budgeting, investing, etc..
I generally don't recommend getting credit cards at this time if you currently have at least 1 & of the following are true, prioritizing the below prior to acquiring a new credit card:
Current interest accruing revolving balance
If you've carried an interest accruing balance on any credit card in the past 1 year,
Committed bankruptcy in the past 5 years
If you've committed bankruptcy in the past 5 years, I generally don't recommend acquiring any credit cards but at least 1 card that you spend $5 on each month with automatic payments in full if you don't have any cards at this time.
Paycheck to paycheck
If you live paycheck to paycheck, without at least 3 months of your income in savings or liquid investments (i.e. stock or a Roth IRA with at least 5 years)
No health insurance
If you don't have health insurance or other health coverage
No auto insurance collision coverage
If you don't have collision coverage or full coverage for auto insurance, own a vehicle, & don't have the savings or liquid investments to replace it for a comparable vehicle.
No life insurance or comparable investments
If you don't have at least a $50k life insurance policy or at least $50k in net worth if you have a family, and at least $15k in net worth if you don't have a family (excluding those under 25 & those who are full-time students even if they don't attend school during the Summer).
No annual contributions to retirement account
If you are over 18, have a full-time job, and don't have any retirement account receiving annual contributions, especially for those with a match available from their employer and/or those whose income is low enough to qualify them for the Saver's Credit.
DTI >50%
Those with a debt-to-income ratio over 50%.
High DTI on car payment
Those who have a car payment & whose car (or other auto) payment is at or greater than 15% of their income if you have a car payment that exceeds 5 years, over 25% of their income if you have a car payment of more than 3 years to 5 years, & payment is over 35% of their income if you have a car payment of 3 years or less, assuming you don't get a new car within at least twice the amount of years after your payment stops (i.e. 6 years for a 3 year loan). If you will likely get a new car within 1 year after your payment stops, I generally don't recommend credit cards for those whose car or other auto payment is >13% of their income, even if that means getting a 20 yr old lower mileage car with a bad paint job (yes, I've done that before when I was a student, paying $600 for the car in cash rather than wanting to take on a loan).
Renting a home in scenario that doesn't justify it
Those who have chosen to rent for >15 years in the same city/county without ever having any intention of moving to a different city/county, without any of the exceptions listed under renting here.
Below 680 credit score
Those with below 680 credit scores (according to a free account on Experian.com ), in most cases, should use either cash or debit cards exclusively, except for $5/month on 1-3 credit cards with automatic payments in full in order to keep the positive impact of those cards on their credit. It's very easy to overspend with credit cards, and the little gains from credit cards will most likely be a net negative in light of the higher propensity to overspend for those with <680 credit scores. For those without any credit cards, it can be a good idea to get one for the $5/month spend concept, but not to travel hack in most cases.
680-740 credit score is questionable
I don't discourage those with 680-740 (according to a free account on Experian.com ) credit scores from travel hacking, but I would say that those in that category should proceed with extreme caution prior to getting into travel hacking. Travel hacking is best for those who never carry a balance on credit cards and who are in a good position of financial management with whatever income they have, whether their income is low or high.
If your only reason for a <740 score is due to credit age, proceed with caution, but you may be in a fine position for a new credit card.
About to make a large financed purchase
While those with no revolving debt (& especially those with high utilization debt) can experience a positive boost to their credit from the acquisition of a new card, and they can experience a positive impact to their interest payments in some cases via carrying balances on new 0% introductory APR card in order to help pay off high interest other revolving debt, if you currently have low utilization, your credit is below 760, and you are about to make a new large purchase using credit (i.e. a mortgage), you may want to forego a credit card until after you've made that purchase. A new application will put a temporary ding on your credit in most cases & a new account will reduce your average credit age, also lowering your credit. Getting $1k in value from a credit card isn't worth it if it means you'll be paying over $1k in extra interest based on a lower credit score when you purchase a home. If you're flying high on an 800 score, on the other hand, it's unlikely that a new credit card is going to make enough of a dent on your credit to make a difference on your interest rate. Typically interest rates are the same whether you have a 761 or an 850.
For those where credit cards are not an advisable option, I recommend looking into cashback debit cards & free debit cards with perks and otherwise getting in a better place financially before pursuing credit cards. See my secured card recommendations here.