Yeah if you play CS or any other fps game anything below 60fps is eww.
Im saying from my experience.
My monitor is 60hz and fps in CS:S is average 170 which is good.
But if i do fps_max 60 i just feel sick when i play it is just , uhh , cant explain.
So i just let it go do its max.
Depending on the code, Locking to 60 might actually make it drop to 30.
Say you're running 60 fps, and locking to 60. That's great! Everytime your monitor goes "SEND ME A FRAME" you're video card goes "Sure, here's the one I just finished!"
But now you install a mod, and you can only get 55fps. What happens if you turn vsync on?
Well, you might think you'll get 55fps, but you won't. The monitor draws frame 1, and when it's finished, it goes "SEND ME A FRAME", but the video card hasn't finished a new one yet. And your monitor is locked to 60fps. So it keeps frame 1 up for frame 2 as well. Meanwhile, your video card has gone "Oh, shit, that frames out of date now, start frame 3"
Hopefully frame 3 is easier to draw, otherwise, it's going to happen again.
Programmers worked around this with double buffering, but that's a harder topic. Double buffering lets us draw to a frame "behind the scenes" and then when the monitor requests a frame, we just pass it that one.
Imagine you have a 75Hz monitor, and the game runs at 100fps.
Video card draws frame 1, puts it on the buffer. Video card gets half way through frame 2. Monitor requests frame 1. Video card puts half of frame 2 on buffer, and finishes drawing it. Gets 90% through frame 3, monitor requests frame 2. 3 moves to buffer, card starts drawing 4, and with the buffer full, the card can wait patiently til the monitor has claimed the frame before hand. This is great, we will max out the vsync.
But what if our fps drops?
You're at 75Hz refresh rate still, but now you're only getting 50FPS, 33% slower than the refresh rate. That means every time the monitor updates the screen, the video card draws 2/3 of the next frame. So lets track how this works. The monitor just refreshed, and frame 1 is copied into the frame buffer. 2/3 of frame 2 gets drawn in the back buffer, and the monitor refreshes again. It grabs frame 1 from the frame buffer for the first time. Now the video card finishes the last third of frame 2, but it has to wait, because it can't update until right after a refresh. The monitor refreshes, grabbing frame 1 the second time, and frame 2 is put in the frame buffer. The video card draws 2/3 of frame 3 in the back buffer, and a refresh happens, grabbing frame 2 for the first time. The last third of frame 3 is draw, and again we must wait for the refresh, and when it happens, frame 2 is grabbed for the second time, and frame 3 is copied in. We went through 4 refresh cycles but only 2 frames were drawn. At a refresh rate of 75Hz, that means we'll see 37.5FPS. That's noticeably less than 50FPS which the video card is capable of. This happens because the video card is forced to waste time after finishing a frame in the back buffer as it can't copy it out and it has nowhere else to draw frames.