There are some players, that have expanded knowledge, but I want to add something too.
Point about softer rubbers does not really work, since softer rubbers are slower. Tenergy 05 FX does not equal boosted Tenergy 05, conversely the boosted 05 is much much faster than the unboosted one, with better spin and especially feel. Somehow when you have 2 same rubbers, boosted and unboosted, the second one would feel dead when hiting ball. So it can sometimes be more controlable though being faster at the same time.
It get´s me to the second point, which I already mentioned, and it is increased speed and spin. On the World Tour topspins "must" fly very fast, otherwise you would not stand a chance. And more spin is always better option.
Third point, that I read somewhere, I´m pretty sure Petr Korbel said that, is that without boosted rubber, table tennis is much harder. That means, with so much training units, players over burden their muscles and joints. Even though softer rubbers might be easier to play, they are not as fast as needed, therefore top players boost harder rubbers. Imagine having Sriver and playing with it strong swing topspins. Imagine the very same thing, just with speed glued Sriver. Much easier play, yet rubber is still same, just with some improvements. Now we are in the speed glue effect era with modern rubbers, but the principle stays the same. We have now even harder rubbers than ever before, such as 05 Hard, Xiom Omega Jing/Jang, Rhyzer 50 etc.
And one more mention at the end, I again read somewhere, but do not take it too seriously. I guess it was mentioned at some Chinese Weibo or somewhere. That said, when Ma Long lost to Timo Boll at 2008 World Cup, it was because he had badly boosted rubbers. They were not perhaps to fast, or were to mushy. Does not have to be true, but boosting is somehow complex method, that can be messed up.
Cheers
