I posted this in another thread but it may have been off subject and/or the thread was dying.

The other day I was tuning up my brothers mountain bike had 9 cogs in the back, and I adjusted it well enough for the chain to move to each cog without flaw however there were still extra shift clicks in the shifter. This puzzled me but I could not adjust anything enough to get it to just have 9 clicks. So today I was adjusting my front derailleur on my Fuji touring bike, 3 rings up front, and although there are only 3 rings my shifter was clicking 4 times. I brought this up to my mom who has a new Fuji road bike and she said hers and her boyfriends bikes do this also and it's probably supposed to happen. I read something on Sheldon Browns website last night on something called trimming so are these occurrences related to that or is this something just different altogether?