Not taken towels for years.
Never had a problem taking a few from the pool at OKW to take to the water parks but last year we were stopped by a CM. Told us we were not allowed to take them anymore, no problem we went to another pool and got them.
We take towels/have them in our Owners Locker because I don't find the Disney towels big enough! Personal though as I know a lot of people just use the towels supplied.
I also use them to hold everything in the case to make it easier to close which is a habit I got from my mum!