As a reed begins to wear out, a trimmer will cut off the tip of the reed, and it can often restore some of its strength. It also works for reeds that feel just a little soft when new. Because it shortens the reed, the cane will become proportionately thicker at the tip and therefore feel harder again. It can prolong the life of the reed or repair a slightly damaged tip. However, this procedure can only be used successfully once or twice.
There are two types on the market: the legendary "Cordier" (good ones that don't shred the tip can be hard to find) and those with a flexible, adjustable knife which cuts cleanly.
To be able to use more of your reeds or to prolong the life of your reeds you should try to learn the art of reed scraping.