I've been playing Dota 2 for a while now. I'm a level 6, so I'm still a noob, but I do have an idea of what's going on.
Anyway, I've been watching some Purge Plays videos. In these, I see him denying his creeps even if nobody is nearby that would last hit those creeps. For example, he is farming in an empty lane, nobody is nearby, nothing is showing on the mini-map, and he still denies a creep.
Why would he do this? Is it just an instinct or is there a good reason for doing this?
Each time you or your teammates deal any damage to the enemy creeps (in this case by last hitting them) you slightly help your creep wave to push the lane towards the enemy tower.
The best place to farm is slightly in front of your towers range of attack,so you are close to safety but without tower interfering with the creeps.
To get creeps to fight there you will have to block your creeps movement as much as you can and then actively hit and deny your creeps as soon as they get under 50% HP to help enemy creeps push the lane closer to your tower.
Once you get the creeps to fight in that spot,in order to maintain that place each time you hit the enemy creep you should hit or deny one of your creeps too. This is known as maintaining lane or creep equilibrium.
There is also a chance that some invisible or hiding enemy hero is there trying to get EXP
You often see him doing this when he is laning as a carry.
By doing equal damage to enemy creeps as he does his own creeps, he ensures lane equilibrium, ie. the lane doesn't push in either direction.
The real goal is so that you can continue farming safely, close to your own tower, but just outside of the tower range so that you don't need to compete with the tower for last hits.
Try it in an empty lobby, it's excellent practice and reasonably difficult, aim for ~3900 gold at the 10 minute mark (which is the average gold you would have if you last hit every creep), and keep the wave in control at the point it first meets.
