Sealing to get better efficiency and a quieter shot. Sealing the breech also means you can shoot with a smaller, lower pressure burst of gas which (although it's hard to prove 100%) does seem to help with shooting more fragile paint. You'll notice the large difference in operating pressures between an Empire Sniper and a CCM gun.
You can take them off and have it feel like the CCM if you so wish. You can also remove the hit man mod, and the pump return springs to make it lighter. This way you get choices. You don't have to play with any of those items.
I can't believe anyone actually feels the ball detents on the o-rings during actual play.
The only time anyone notices it is when pumping slowly without playing. I've never noticed it in play.
Anything I ever design is intended for the best results under playing conditions. Not you tube videos.