Light Infantry vs Skirmishers

What's the difference between these two abilities and how are they best used? I am pretty new at this, and also Napoleonic Warfare in general (just recently I started reading up on it)

Thanks!

"Light infantry behaviour" means your men spread out and kneel down. This way, they take fewer losses and no friendly fire. This can be used by putting them in front of your line infantry, so you'll have double the firepower (line and light inf).
"Skirmish" means that your men run away if another unit tries to engage them in combat. This is a bit of a double-edged sword: firstly, you won't be able to control them anymore if an enemy is near them (in this case, the skirmishing takes precedence and you have to switch it off before giving move orders again). Secondly, once the enemy has stopped pursuing your men, they will stand still without turning around, so they'll have their back to the enemy and won't fire anymore.