Some people (mostly ork players) like to get Independent character rules wrong regarding joining and leaving units.
It is common for some players to attach Ghazghkull to a unit of 30 boys... which in turn causes the entire unit to suffer from slow and purposeful. Those players often then declare that Ghazghkull is leaving the unit to trudge ahead. Let's say for instance that he moves '4. They then take the boy unit he was with and moves them up '6 and re-attaches Ghaz to them. This is not legal....
An independent character only counts as having left a unit if he is out of coherency with it at the END of the movement phase, so he can't leave the unit and rejoin it in the same turn.
This also means that should you join a normal infantry IC to a squad of jump troops, the jump troops may only move a max of '6 in the same turn the IC left.
Some people also have a tendency to 'say' an IC has left a unit, but if he ends his move within '2 of another unit, he's a part of it regardless of the intentions of the controlling player.
Anotherpoint to remember is that if you have an IC as part of a heavy weapons squad and then move him out of of the unit, the heavy weapons team still counts as having moved and so can't fire.
These are just some things to remember, especially at tournements, where Ghaz getting across the board one turn sooner can be huge.