This article is from the MachTen & CodeBuilder FAQ, by Jaime Julca firstname.lastname@example.org with numerous contributions by others.
When MachTen is running, users have full access to Macintosh Finder and
could simply run Macintosh programs. If MachTen is installed on a machine
that will be shared by users who do not want to get involved with UNIX, they
can simply use the Macintosh as a normal Mac, and not start up the MachTen
application. On the other hand, if you always want to use MachTen, you can
set your machine up so that the MachTen application comes on automatically
when the Mac is powered up. Even with this setup, you can easily toggle from
Mac applications to UNIX applications.