In most cases the game warns you with the exception of certain bigger changes (i.e. sex-changing characters which is kinda obvious). I know of a few that kinda apply. I don't know how far along you are so I'll try to be vague.
One I do know of though is with Azzyran. If you do the corrupt end to her questline it becomes impossible to recruit her as a companion but she can still be interacted with in the hive.
There is also a unique weapon called the Dawnsword acquired during Ryn's questline, specifically
The Demon of Ice
at the end of Act I
. I don't remember exactly how it works but there are two versions of it and which one you get depends on your choices and require different levels of corruption to use. Each version also has its own achievement tied to it when acquiring it.
Another one that is kinda along the same line is a certain genie character can provide unique boons but depending on your choices you can lose out on those.
