What is found in these locations varies. They may contain squadrons of pirates, large 'wanted' cargo vessels (which you can destroy and steal the cargo without becoming wanted yourself) and sometimes just empty space with low value cargo laying around. Typically these areas have more than one bad guy, so you can visit these locations without being attacked (as long as you don't have cargo) and have a look around, but bounty hunting or piracy at these sites may require a combat focused ship due to the random nature of the encounter (there may be Anacondas!).
Assassination missions require you to visit these sites in order to locate the target. Usually you will find a damaged trade convoy that will tell you the last known location of the target, but are usually no more specific than a system.