It's very funny when people proclaim boosting illegal. Somewhere along the line a myth aroused that boosting was illegal, but that only holds true to boosting the topsheet. There's no law specifically stating that one cannot boost the sponge and there is no law that states boosting cannot be done period. The law specifies that no use of anything with VOC's is allowed and that's what makes rackets illegal. The other illegal limitation is the 4 mm rubber thickness. Boosting too much will create more often than not a problem with thickness or bubbling because the booster has soaked through to the adhesive on the topsheet's pips.
I think that a lot of players also have this misconception that boosting makes the rubber ridiculously faster and spinnier, but that's not really what's happening. At the highest levels of play the amount of speed and spin the booster provides is minimal compared to the amount of control it provides. The rubbers professionals use produce loads of spin and speed on the ball, but the booster helps to soften the rubber to their preference and thus gives them much more control on their shots. High level players need customized equipment because at their level it's no longer about who's stronger or who has a better shot, it's much more about who can out place the other and for that, control is really needed.
Look at any other sport. Badminton players tighten their rackets to their preference, Baseball players oil their gloves and choose their bats just the way they like them. No matter the sport professionals will adjust their equipment the way they see fit because it makes them better athletes. Table Tennis shouldn't be any different. The VOC call was good for player's health, but the laws still allow for boosting that doesn't involve the topsheet.
I know for a fact that the Chinese players, the German players, and pretty much every player in the top 100 excluding maybe a few boost their rubbers legally. Most of the players that do well in the sport either through University or professional play should boost the rubber and really research it. It makes the rubber play to your standards and keeps all of the aspects you want in your rubber while avoiding some of the more unnecessary ones.
Here is the law:
"Law 2.04.07 - The covering material should be used as it has been authorised by the ITTF without any physical, chemical or other treatment, changing or modifying playing properties, friction, outlook, colour, structure, surface, etc."
This applies to the topsheet and the sponge. The word "covering" is being used to refer to both the topsheet and the sponge as what is being placed on (and therefore covering) the wood. Once the ITTF has approved of a rubber, chemicals cannot be added to it that are intended to change its playing characteristics.
Here is Greg Letts writing on the subject on about.com
"Well, so what, you might say? That little sentence above is the rule that will remove speed glue, boosters and goodness knows what else from our sport in one fell swoop. Here's why:
Speed Glue - speed glue will no longer be legal due to the changes it makes to the sponge of the covering material, as well as the stretching and tensioning affect it has on the topsheet. So say goodbye to speed glue.
Boosters/Tuners - similar to speed glue but without the VOCs, boosters and tuners will be outlawed for similar reasons - their effect on the sponge and topsheet. There's no official word from the ITTF on this issue yet - stayed tuned(!)."
Here is the link to his full article.
http://tabletennis.about.com/od/speedglue/a/ban_speedglue.htm
But, boosting is against the table tennis rules and above is the rule.
