Depends on the quality. I had a cheap Apple knock off one I got online for $10 and it demagnetized all my cards. After that I purchased one of the Apple leather ones and have been using it for a long time with zero issues.
I've had some parking passes demagnetized with my Moft MagSafe wallet/stand. The parking garage person just let me leave for free each time. After about 5-6 times, it kind of clicked that my MagSafe wallet was causing it and I immediately stopped putting them in there. At least the wallet ended up paying for itself at that point.
Never had any issues with credit and debit cards though.