Originally Posted by
Aristokrata
No matter how much I read on trimming, I can't seem to grasp the what it's trying to accomplish. What is the point of the half shift? Because; when my shifts miss, the bike is just caught in a neutral state where the pedals row forward freely; sometimes the gear will "eventually" catch, and other times, I will gear up again, and then back down to get the gear I was supposed to be in. The miss-shift usually happens on a very medium cassette wheel, for flat road; so, it I wouldn't be on any extremes for cross chaining from the main chain ring.
The idea of trimming the front derailleur is to prevent the chain from rubbing against the slide plate if you have the chain "cross-chained". That is...running in the small ring on the front and one of the smaller sprockets on the cassette. In these scenarios, you can "half shift" the front derailler to the right, which moves the cage to the right to prevent chain drag. This is sometimes perceived as a missed shift.
It sounds like your chain may be skipping teeth on the cassette (pedalling forward "in neutral"). That's probably a tuning issue requiring a bit of adjustment with the barrel adjuster. There are a lot of YouTube videos that illustrate this. Park Tool has some very good ones.