I use them a lot. I made a bed cover for my mother out of my stepfather's shirts after he died. She and "his" cat use it almost every day.
A local thrift shop has $2 days --- what you can fit in a bag they give you for only $2; I pick up all the cotton or wool (they can be felted!) XXL shirts I can find. There's a lot of usable fabric in the larger sizes.