How To Boost Or Reduce Parts Of Sounds
Let's say that you were doing a voice over a backing music track and you wanted to reduce the volume of the music when the voice over starts. Instead of manually adding and dragging points, you can use the Boost or Reduce feature.

Make a selection on the music track that corresponds to the time of the voice over.

Now click Ctrl+Alt+S four or five times and the volume will be reduced in the selected area (boost or reduce the sound until it sounds the way you want it).

Alternatively, you can reduce the volume for the selected area by clicking the Sound menu, followed by clicking Reduce, followed by clicking either -1%, -5%, -25% or -50%.  

Boost works in the opposite manner and raises the volume for selected areas.  

Boosting or Reducing Pan, Low Pass or High Pass Filters
You can also boost or reduce the other envelope types by choosing the correct envelope type on the toolbar and then using the boost or reduce commands.

Keyboard Shortcuts
The keyboard shortcuts are designed so that you can use the mouse to make selections and with the hand use the keyboard to boost or reduce.  Simply hold down the Alt and Ctrl key, make selections and push either W or S for either a 5% boost or a 5% reduction.

Here are the actual keystrokes that correspond to the boosts and reductions:

Alt+Ctrl+Q Boost 1%
Alt+Ctrl+A Reduce 1%
Alt+Ctrl+W Boost 5%
Alt+Ctrl+S Reduce 5%
Alt+Ctrl+E Boost 25%
Alt+Ctrl+D Reduce 25%
Alt+Ctrl+R Boost 50%
Alt+Ctrl+F Reduce 50%