If you have enough memory, for e.g. your 4 gb, swappines will have no impact to system performance at all, because in that configuration most likely your system wont swap at all (or just to reserve mem-space). if you have few memory swappines may have impact to system performance. But its kind of a religious question with endless debates which value should be recommended. Alan Cox recommends a value near by 100. Other Kernel-Hackers recommends very lower values (the ubuntu default of 10 is often recommended). But from my experience it does not make a feelable difference in performance at all. So you could leave it by ubuntu default value (60) or choose the ubuntu recommended 10 for desktop systems.