Pros
Even the part time pay at UPS is phenomenal, almost enough to live on as a single adult with no dependents. The benefits gained after a year are also great, including full health insurance and $10 co-pays. Being on the inside will also get you a leg up into a full time position as a driver if you want it.
Cons
If the managers suck (and even one terrible manager can do this) it's not worth the stress and physical danger you will be in. You may end up risking your life, and this job isn't worth that. At lower seniority levels you may also be laid off at any time, making the great pay that we get almost irrelevant. If you can stick it out and have a good management team, it gets good, but only because of seniority pay increases and more job security. There are no opportunities to advance from this position except laterally into a driver position and very rarely a part time supervisor (and you lose your benefits in the latter case).