Simply put.
You can create higher leech tensions with less pull on the sheet line as the pully setup looses alot less force on bending the sheet around the sheeve. One great way to feel this to pull the two block apart and see how much force is needed to do that. Any mainsheet that uses a plain 8 mm sheet will require ALOT of force to pull the two blocks apart. When using a tapered sheet this force is MUCH less.
In lighte winds the sheet will continue to run smoothly because there is so little drag in the system, so improved control here.
The thin line are less likely to rub against one another when sheeting tight = again less loss of force in the system.
A small amount of weight savings.
By having a more efficient force creation often you can drop a purchase. Meaning go from 8:1 to 7:1. => cheaper blocks, less sheet line etc.
All in all there are only advantages, as long as the taper itself never passes the ratchet wheel.
This is one of those things that everybody should have on their catamarans.