Depends on the gift. I'd be iffy on getting rid of stuff with sentimental value or that was handmade. Other stuff is fine though, like the toiletries that relatives get me as gifts that I'll never use because I don't like the smell of them. I'm only a packrat with sentimental stuff, I rarely keep books after I've read them but I have about a decade's worth of christmas and birthday cards in a box somewhere for example.

On the other hand I wouldn't tell someone to keep something if they really wanted rid of it. That's their call.