Is it impolite to crosspost someone else's post to another community on Lemmy without saying anything?

I feel like on mainstream social media this is done pretty thoughtlessly and it's a norm but on Lemmy, with the much smaller userbase, I kinda felt like... it's like riding on someone else's coat tails? Or is it just me?

Edit: I specifically mean the Crosspost function.

Edit: of course if it's artwork or text, obviously then I'd make it explicitly clear it's not mine but I mean news articles, memes, things like that.