I want to get a slip-on pipe and rejet the carb and remove the airbox lid and all the good tricks====but I dont wanna bypass the smog/emissions system unless I have too=====basically my question is=Will not removing the smog stuff affect the performance of my add-ons====or are people doing this cause it elminates clutter------or is this like something one guy did who told another who told another then it became standard practice? ====== and no this wont be my last stupid question I ask )

 

You can leave it. It also helps with temperatures inside the pipes. It will be hotter if you leave it.

Just take it out it's not a big deal.

 

The removal of the smog stuff is basically as you said anti clutter, does over heat the head pipe and turn it blue. It's only a couple of hoses. But critical if you want to fit a bigger tank.
Rid off the clutter make your bike your own.

 

Your lawnmowyer emits more emissions than your bike. No worries.