Splitting and joining surfaces vs breps

Hi everyone,

In my definition I have one surface which I am splitting using a set of curves. Then I select some of the resulted fragments by using collision component with another set of curves. After that I join each group to form a single curve. When I used surfaces and region union, many problem appeared. Collision failed to recognize all fragments and some regions didn't unite with others. Then I replaced surface with brep and region union with brep join and everything thing went smoothly and took much less time to compute. 

My questions:

What is the difference between surfaces and breps?

Why there is a change in curves directions?

Is there any other way to make the same routine with less time as the actual definition is more complicated than the one given below?

Thank you,

Ramy