Question

Is there any difference in performance when you break down a stored procedure into multiple procedures instead of having a big procedure?
Which one is faster?

For example:

mainSP
  callSP1
  callSP2
  callSP3
end;

rather than:

SP
  .... 
  ....
  ....  

Answer 1

Any performance benefit would be in very rare cases, e.g. where the main proc is being called many many times in a loop and each individual iteration does not take much time.

Most of the time the maintainability of having your program broken down into logical steps will far outweigh the minor performance gain that might be had.

As has been stated before, benchmark and test – unless you see a significant benefit, go for maintainability – future developers will thank you!