Couple reasons I rarely use debit cards, I use a credit card and pay it off every month:
If it gets stolen/someone else uses it, all I need to do is tell my bank, and since I have not paid the debt, I am not out any money. It is on the bank. If I was using a debit card, it may take a month+ to be investigated/money returned.
Emergencies/availability having available credit is useful, most of my money is in investment accounts, even if only to get higher money market interest rates. I can transfer to my bank account, but that takes time. Having ~10k in credit available for if I need a last minute plane/hotel/hospital is good in an emergency. Once I'm safe I can move the money around as needed.
Cash back, coming from the USA credit cards give me 2-3% cash back. That is significant considering I use them for all purchases.
I do not believe that credit card accounts have a negative affect on mortgages. They are different types, with credit cards being revolving. As long as you are paying it off and not maintaining a valence, then it should only be a net positive (shows credit history of paying debts).