When I did my coldside supercharger, I took it out because I had an intake where it should be. I lived that way for about 3 months before I put it back on the hotside of the bay. Here's my observations.
1: on OBDII cars, you'll get a CEL very randomly and not very often without the charcoal canister there. Once the ECU sees it, it won't check for it again, but if you reset and don't have it in place, you may get a code within like 500 miles. It takes a long time to show up unlike most other emissions codes.
2: it's attached to the gas tank. Fumes from the tank get trapped in the charcoal and then sucked into the intake. You can follow the line from the gastank, up the frame, and into the bottle. One small line connects it to the intake through the evap actuator. One large line goes out the bottom and back to the frame and dumps to the air right near the passenger side motor mount.
3: You'll get a large gas smell on warm days after you park without the charcoal canister. My garage stunk of gas for 3 months. For this reason, I put the thing back in and ran lines to the other side of the bay.
So that's what I learned about the cannister. Ugly thing, but it does its job.
