Perhaps you’ve been delaying upgrading to High Sierra until some bugs are worked out. Or maybe, like me, waiting until APFS has got some real world mileage before jumping in. I was waiting particularly on the advice of Bombich Software who pointed out the real lack of knowledge and documentation about APFS. Their advice was to wait until 13.1 was released.
13.1 has now been released so I am going for it (with a couple of backups at the ready to be on the safe side).