With the exception that I remember (or misremember? I`m going to
have to check soon!) the two sections in the reverse order, and that I hadn`t yet learned a trick or two that he mentioned above (but they
are good ideas; I`ll have to remember them), I agree with what
@pware said above. You can even place
track into a session layer, but only if you want it to exist in that session
only. Rare.
Very rare, but doable. Trouble is some people do it by accident, and
that is bad.
Very bad. I`ve heard of routes where
everything had been placed in the session layer(s), the (empty!) route uploaded somewhere, and the session (where
all of the hard work was stored) deleted. Fun. Not. Be
careful!
Good names for some of the layers (should be obvious what goes in each) include Track, Roads, Buildings, Signs, Plants, Animals, Industries, Scenery (Other), and any other category of stuff that you want to be able to (un)lock as a group when editing something (else).