This plugin is in fact two plugins in one:

1. It can calculate a power track for your activity, i.e. a track of the power you deliver at every moment of your workout.
   The power calculation is based upon your particular speed, the climbing speed and the influence of wind. It considers parameters of the athlete and your equipment (weight, rolling drag, position on the bike, ...).
   Hence, this plugin is "poor man's power meter".
   The calculation was designed for biking, but thanks to David C. Hall there are custom configurations that adapt this plugin for running as well. This is covered in http://sporttracks.zonefivesoftware.com/Discussion/viewtopic.php?t=2727.
2. It can fetch weather information from the www.wunderground.com network of weather stations all over the world.
   The weather information is stored in your SportTracks logbook. It is used for power track calculations and can be displayed on an activity detail page that is provided by this plugin.

So, even when you're not interested in the power of your workouts, you can use this plugin to keep track of the weather conditions during your workout.

You can find detailied information on the plugin home page at www.sporttracks-plugins.de/SportTracksPlugins/MyPlugins/GPS2PowerTrack Plugin.