I assume you're talking about Shimano's 12s XT rear derailleur. For disambiguation, 8100 could also refer to the 12s Ultegra groupset. However, that doesn't have a clutch, and I believe Shimano doesn't intend to put a clutch on its road groups (in contrast, SRAM has clutches).

When you ride over rough terrain, the chain bounces a lot. This increases the odds of the chain falling off the front chainring. Adding a clutch to the rear derailleur means that the derailleur cage can't swing forward - this is why you need to deactivate the clutch to remove your rear wheel. This decreases the amount by which the chain can move when you're going over bumps, which decreases the odds of the chain falling off the front - particularly helpful for 1x groups.

Hence, the clutch does nothing to affect the shifting at all. It most likely does not increase drivetrain friction. It improves chain retention and decreases chain slap in rough terrain.

I assume you're talking about Shimano's 12s XT rear derailleur. For disambiguation, 8100 could also refer to the 12s Ultegra groupset. However, the Ultegra group doesn't have a clutch, and I believe Shimano doesn't intend to put clutches on its road groups (in contrast, SRAM has clutches, all of Shimano's gravel groups have a clutch).

When you ride over rough terrain, the chain bounces a lot. This increases the odds of the chain falling off the front chainring. Adding a clutch to the rear derailleur means that the derailleur cage can't swing forward - this is why you need to deactivate the clutch to remove your rear wheel. This decreases the amount by which the chain can move when you're going over bumps. In turn, this decreases the odds of the chain falling off the front - particularly helpful for 1x groups.

Hence, the clutch does nothing to affect the shifting. It most likely does not increase drivetrain friction. It improves chain retention and decreases chain slap in rough terrain.