ATM Benefits of a 2" focuser

["Anderson, Jay" <andeja@mail.va.gov>]

I can see in my ray trace program that there are some real benefits to
going with a 2" focuser on a 12.5" reflector or larger.  Also, there are
benefits to having as low a profile focuser as possible as a smaller
diagonal can be used and thus reduce obstruction of the primary mirror
thereby lessening diffraction and so improving contrast....yaady yaady
yaada..

Anyway, seems that people often use a 2" focuser and then a 2" to 1.25"
adapter so they can use the less expensive 1.25" eyepieces with it.  My
question is... aren't they negating the benefit of the larget diameter
focuser tube?  Wouldn't it be more beneficial to use 2" eye pieces, and
2" barlow, etc with the 2" focuser?