What exactly does Optimizing the level do? Is it good or bad? Has it changed in Dark 2.42? Potato?

I don't remember it doing anything bad personally, I don't believe its changed. but it is something you should do before releasing a level otherwise I woulden't worry about it

What exactly does Optimizing the level do? Is it good or bad? Has it changed in Dark 2.42? Potato?

It's good, it's very good!! It's smth like defragmentation for level geometry. As DE build cells for brushes at portilizing, for time pass it becomes very stupied. Look here, this are what DE made with 2 simple brushes:

Image: http://www.kachalka.com/images/n5pfa2bpi08srcy29qw.png

7 cells, 22 portals, and after optimization all was combined into 1 cell (ya - 1 cell for 2 brushes !! ):

Image: http://www.kachalka.com/images/266sv09m36bkxxjj3qo3.png

So Optimizing reduce number of cells that allows you make you levels larger and makes them work faster for users.

Would have thought ne1 could have worked out that was short for 'something'.

Smith-like defragmentation? Smuth-like defragmentation? What?

I'm sorry, my english isn't very good, I mean - ... something like defragmentation ...