Originally posted by Macdallan:

I don't think that's always better. I often prefer hitting two trees at the same time if I can. It doesn't seem to divide the damage by the number of things you hit, just reduce it a bit. I could be wrong but it seems faster to hit two trees at once than to chop them down separately.

Of course if your aim is only to cut one tree down then yes, making sure you don't hit other things is going to make it faster.

The main thing that i wanted to point was to avoid hiting the floor. :)