For the most part I think they do a good job of balancing the game, but the community itself is a malignant tumor. They banned Recycle + Leppa because of the ability of one pokemon to abuse it, and their reasoning was "Get over it, it's not competitively viable, thread locked", seemingly forgetting that at one point video games were about fun.
I also remember someone trying to discuss Protean Kecleon's viabilty in OU, he even posted a number of good sets, and the very next post the mod locks the thread because Kecleon isn't a member of the top-tier circlej***.
they're obviously not needed, but if people like playing that style better they have every right to enjoy it. their rules have never affected me and i see no reason for friction to exist between people who play smogon rules and those who dont.
It's just a set of rules to create balanced play within its own system. It creates a different level of balance and therefore a different metagame than the standard ruleset. I don't care for it but that hardly matters since I don't play simulators anyways. (Mind, there's nothing wrong with doing so. It's a quick and easy way to gain experience in competitive play.)
The only impact it really has on me is the influence research there has on my own pokemon builds, as they have a lot of good breakdowns. Still, you always have to keep in mind they come from a non-standard metagame where certain powerful things (like Moody Smeargle) have been banned. But you should always put more thought into your pokemon builds than just culling them from a site regardless.