It makes the tip more consistent. It also lowers the BC, since it widens and flattens out the tip.
I use a Widden bullet tipping die for my 6.5mm 140 VLD's. It closes up the hollow point, which makes it more uniform and increases the BC. I gained right at 5" less drop at 600 yards with a tipped bullet compared to a non-tipped bullet. And it shot slightly tighter groups. My G7 BC went from .313 to a .323 G7 increase, which is just over a 3% increase in BC. This was with my 260 Rem at some faster speeds. Now I just load the factory bullet, since I haven't taken the time to point them. I'd recommend pointing the bullet over trimming the point, though.