Strava sync

Can anybody explain for me the fololwing phrase: This will remove Xert activity Links and Breaktrough information added to your Strava activities by the auto update feature. What are activity links and breaktrough information?

If you have the “Show Breakthroughs on Strava” toggle switched to blue (on) your breakthrough activities (only) will show up on your Strava feed. If you wish to remove all of these from the past, clicking the “Revert…” button will remove them.