I have a selection of credit cards for different purposes - a couple are very cost effective abroad (Halifax Clarity and Saga), one offers points or rewards on all purchases (Tesco) and the other is the key that unlocks an excellent free current account banking service (First Direct).
I pay each card off in full at the end of any month in which it is used - I've never paid a single penny in interest on any of them - but have gained £100s in freebies, discounts and kickbacks.
I also carry much less hard cash than I would need if I didn't use the cards - and therefore am not tempted to spend on impulse because I feel flush.
To me, the imprudent person is one who is so bound up in "credit cards are the invention of the devil" that they actually cost themselves money by sticking to cash (or debit cards) only.