ORIGINAL: daven
Sub trim is for people to lazy to adjust the clevis manually
My planes use very little movement, so I guess I'm one of the Lazy ones. It is very easy to use sub trim to adjust a surface.
For planes that require full movement on the servo, you should fix it mechanically for maximum throw.
Read carefuly... Sub Trim is for centering the arm on a servo as some servos are not quite centered from the factory... This is normaly done before any control surfaces are connected to the servo... It is not intended for trim purposes... As a last resort you might try reading the manual... Sub trim has nothing to do with adjusting the clevis manually