I hate reserved seats. Most of us would like to be able to get on a train at the time of our choice. When we buy the ticket we don't know what time our return journey will be.
It's a real pain to get on a train and find every seat reserved, to find empty reserved seats and people standing because of that.
There are empty reserved seats because passengers are offered a free reservation when they book, so they get one anyway on any train which might or might not be the train they go on.
Train companies should be obliged to leave half of every carriage unreserved, or they should charge for reservations, or only permit reservations for people travelling in groups.
If all the seats have tickets, and one of them is empty, I sit in it. Of course if someone comes along and says it's their seat I have to get up.