I try not to if I stumble onto it after its abandoned. Its kinda like starting a new tv show that was already cancelled part way through the first season
It can be fine if you go into it with your eyes open. If they where in a good state when they were abandoned then they can be worth it without any expectation of a follow up. Given how common abandonment is playing an unfinished game that just recieved an update could be the same, there are no guarantees you'll ever get a follow up.
I do play them, for nostalgia mostly or to check if I missed an update before it was abandoned and I still have a little more content to play with.
I have also went out of my way to check ones that I didn't know just to see if they were good or not.
Checking is always good since you add that content to your memory if is good and learn if is bad.
But obsessing over it is meaningless. Same with those famous dreaded long mile games that get a meek update every six months (summertime saga, innocent witches etc)
I have no problem with playing abandoned games, although obviously I prefer it when good games are still being developed, or when they have a proper(!) ending. The journey is the destination.
I mostly only do it for devs that I've played works from that are either still in development or are already completed. I like to see and judge for myself if abandonment was justified or not when it comes to quality.