BlueTracker

Throughout the 10.2.5 PTR, your XP was reduced by 20% per follower, so if you ran a dungeon with two friends and had two followers with you, XP was reduced by 40%. If you went in solo with four followers, XP was reduced by 80%.

When 10.2.5 goes live in this region, each follower will cause a 5% XP reduction. Your party of three players and two followers should see a total of 10% reduced XP, and solo players with four followers receive a 20% reduction.