Yeah, VSync is short for Vertical Synchronization and what it does is prevent "frame tearing" which shows as horizontal lines when the screen starts to draw the frame sent to it by the GPU, but while it is drawing it, the frame buffer info changes, and it starts to draw the next frame.
This is avoided by syncing the frame output to a frequency that the display can support. Thankfully, most modern flat panel displays support a wide range of frame rates, typically 60 FPS is the "root" frequency and the highest they can use, but they usually also work with 50 FPS (which is part of 1080p50 definition, one of the competing HD formats), sometimes 45 FPS, 40 FPS, 30 FPS, 25 FPS, 24 FPS, 20 FPS, 15 FPS, 12 FPS, 10 FPS, 6 FPS and 5 FPS.
Basically, all the factors of the highest frequency are supported by default. That means, if the highest frequency is 60 Hz...
1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30 and 60 Hz frame rates are all supported with no screen tearing.
If your frame rate is 12, that means you get five identical frames, then it switches to next, and since 12 x 5 = 60, it syncs up perfectly with the native refresh rate of the monitor.
The non-factor frame rates like 50, 45, 40, 25 and 24 FPS are sometimes added by manufacturers to reduce the "gaps" between supported frame rates on the high end of the factor list as well as expanding the support for different video formats.
Video capture programs such as Bandicam limit the frame rate to the configured frame rate of the video capture. If you have set it to capture video at 30 FPS, it will limit frame rate to that value.
Whether limiting frame rates manually does any good is dubious. I suppose it can enhance stability on the game when the application has a set amount of frametime to calculate each frame, but if it's doing it with CPU time to spare, you're essentially limiting your gaming experience for no good reason - and, of course, when the computer can't do it fast enough to render the game at 30 FPS, it will slow down regardless.
I personally find it much more sensible to force VSync on GPU control panel, and let the game run as fast as it possibly can.
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