What is the benefit of sticking to one class and not choosing a second? You are not forced into putting points into your second class, so why would this be an issue? Example, take Monk and just use Rez. No need for points.
Maybe I am missing something?
Why One Class
Velric Shadran
Zai
Roleplay reasons. Personal preference. Not wanting to have to explain your build all the time (E/Mo for example "are you healer?").