I've been taken to task privately for only pointing out the good things about an LSD, so to even out the sheet, I will point out some weaknesses:

1. They do not lock 100% like a locker and therefore will not be as effective in extreme situations

2. They are likely not as strong as the best carrier replacement lockers such as the Detroit Locker or ARB. The Tractech truetrac indicates it should not be used with tires taller than 33".

3. If used in the front, it will affect steering by making the truck understeer somewhat.

4. It will place more strain on your steering components than an open diff, although not as much as a full locker.

...I can't think of anything else.

-P