Many people occasionally want to select what gear they're in to improve performance, ie: downshifting to go down a steep grade, downshifting because they're about to pull into the passing lane.Downshifting to go into the passing lane?
By downshifting you can accelerate quicker, thus passing the slow car faster. Don't want to stay in the oncoming traffic's lane any longer than you have to :-)
[link|http://www.standardshift.com/faq.html|Learn to Drive a Car with a Manual Transmission]
Downshifting
You'll want to downshift when heading down a steep slope to reduce riding the brakes or when greater acceleration is needed.