I just leave my feed on All to see a bit of everything, but it drives me nuts when I see someone either post the same link in quick succession to 3+ instances at the same time, so they all end up next to each other on my feed, or you post several related posts (photography, articles etc) within a few minutes so your name and all your context blocks out a large chunk of the All feed, I downvote each post, then block you as a poster, and each of the instances as well. I understand cross posting and wanting to create content for the community is something you want to do to get the Lemmy ball rolling more, but spamming is just extremely annoying, regardless of the content.
It actually wouldn’t be tough at all to do a simple form of it. Lemmy already detects cross-posts and Lemmy web shows a link to other instances of the same link from the post page. It could have a setting to say “only show me the first of any given cross-post in my feed”.