desired FPS, affect performance ?

[s4m_ur4i]

Hello, not getting it out of the doc.
when I set: 

game.time.advancedTiming = true;
game.time.desiredFps = 50;

My Game runs with 50 FPS (instead of 60). That's what I intended to do.
Just because I do not need more FPS. So does this REALLY affect performance?
When doing much calculation and drawing, is lagging reduced by 50FPS (desired) then 60?

kind regards