Even Greener Pastures

Two big things are they do not need "probable cause" and they do not need search warrants.  If you jump bail they can use any means necessary to hunt you down.  I don't think that really includes violence (unless you resist).

In the movie "The Fugitive" Federal Marshalls are after an escaped convict.  In this case since the convict committed a violent crime the Marshalls were allowed to consider him "armed and dangerous" at all times.  Basically shoot first and ask questions later.