That depends on your costs associated with a new signup. If they're nominal, then don't ask for a credit card, you're almost guaranteed a better conversion rate

That depends on your costs associated with a new signup. If they're nominal, then don't ask for a credit card, you're almost guaranteed a better conversion rate. If they're high (you often need to handhold new users through some kind of setup, your service is attractive to spammers or some other bad element you'll have to clean up after, it's resource-intensive to service each user, etc) then require a credit card to filter out all but the most committed prospects.