If a post is boosted by a lot of people, you may see it repeatedly in your timeline. This can be annoying if you’re tired of seeing it.
There is already a feature in Mastodon to prevent this happening, called Group Boosts, and it is on by default, you don’t need to do anything to switch it on. Unfortunately, it is hardcoded to allow boosts to repeat after 40 other posts have been in your timeline. This limit worked okay in the early days of the Fediverse when things were quieter, but nowadays with millions of people online you are a lot more likely to see repeated boosts.
This 40 posts limit cannot currently be adjusted by users or admins, but hopefully the developers could allow this to happen. If you are comfortable using github, you can vote for this limit to be adjustable by giving a thumbs up to the first post in this thread ⧉.