What does a units level property really do?

Ok I know it sets the units level but what does changing the units level effect? I tryed copying a unit and making one level 1 and the other level 10 but the units Attack and Defence stayed the same so Im just confused as to what its for since theres a Constant that sets a units MAX level.

Thx

It changes how much experience the unit gives to heroes when killed. (If you use normal Blizz exp systems)
It also changes its order in the OE.

Sorry OE ?

I think he means when you drag select units, the box where all their icons appear. The higher the level, the further up on the list they are. Try it sometime, Select 1 knight, 6 footmen, and 5 riflemen. I think the knight will be at the top of the list.
Also, level affects whether certain abilities can be used on that unit, like charm, doom, and transmute.

no he means how much experience they give to heroes when killed. Higher level gives more experience.

OE = Object Editor

No, the "Stats - Priority" field affects the position of the unit in the group.

Right.
I'm talking about in the object editor.

If you change a unit's level, it changes their order in the object editor and organizes unit's of similar base by level.
That way you could have 50 units based on a footman and still maintain some sort of organization.

Correct.
Though this only applies to using Blizzard's experience system.
If you triggered it, you could viably change it still.

it will also affect spells. like Charm and Transmute too i think

Little late, I already mentioned that oNdizZ.