When I started learning Blender there was no left click. The decision was made for me. I didn’t think too much of it because I figured that must be normal.
It wasn’t until a few years later when I was working in Maya that I realised how clever right click is.
Left click is used for everything and it really slows you down if you need to select something or move something that behind a widget. You have to press a whole bunch keys to change the manipulator or select somewhere else and then try to select what you wanted.
With right click, you do not have to do anything special. You just keep working.
I think I explain more in the article Phil linked to. There’s one other reason they changed the default with I wasn’t aware of at the time and that was for the people who use Blender with a tablet or stylus pen. (left click is better for them)
If you have trouble with the link Phil posted – try this one: left-click-or-right-click
(I’m getting a proxy error with the one above – but this is the same article)
