-You can use dockable forms with _screen can't use with main form
-You can do visual designs with main form can't do with _screen. You have to do some coding
-If you used modify file or same command's you have to correct them with "in" clause like :
old:
modi file mytext.txt
new:
modi file mytext.txt in my_mainform

-If you want a statusbar you have to use microsoft statusbar control with main form.