I noticed this while visualizing juke spots today. Probably common knowledge to many, but who cares.

Have a look at this picture:

The red line is the one that the hero will be following. As you can see in the yellow circle, the hero will walk right up to the tree, then make a 90° turn to walk around it.

It's not entirely consistent, but this happens when you let the pathfinding work in a way where your hero has to briefly increase the distance between the point you want him to walk to and his actual position. As you can see, this is the case here, since the hero has to walk in this little "S" shape to get to his target.

Now compare that with when you set the target in a way where your hero does not have to walk around something:

The hero takes a much more direct path, with no 90° turn.

I took a video of this path being walked in both ways, and the more direct way was ~5% faster.

This is the reason why, if you watch a pro/good players player perspective, they spam click instead of clicking once farther away. It manipulates the pathfinding system into giving you a path that is more direct, since it recalculates the path along the way. When you're getting close to the 90° turn, it recalculates the path to not have the 90° turn anymore and use the more direct way.

So to take advantage of this, don't walk by clicking once, keep clicking. There is a handy setting in the advanced options called "Auto-repeat Right Mouse", which automatically spam clicks the right mouse button when you hold it down, so you don't destroy your tendons as much.