The layout.gadget is a 68000 binary with V37 support code in it. This means
that it will work on any machine with at least OS 2.04 on it. However,
because Intuition V37 does not support some features the layout.gadget uses,
it has to kludge a few things. These kludges are contained within an OS
version check, and are fully OS legal. They will not be used on a V39
machine. Obviously these checks can slow things down a bit.

To rectify that, layout.gadget.020 is a 68030 optimised version that
requires V39. It will refuse to work on a V37 machine. However, it WILL
work on a 68020, regardless of being optimised for a 68030. Because it
requires V39, it also uses Exec memory pool functions directly instead
of the linked lib versions. This is another reason why it is faster.

In short: if you have 68000 or 68010, OR if you have OS 2.04 or 2.1, you
have  to use layout.gadget. If you have 68020 or better and OS 3.0 or
later you can, and should, use layout.gadget.020. The V37 version will
work just like the V39 version would, but it is a tad slower.

You do want all the speed you can get, don't you? :)