Vsync is lightweight in most cases and it can even improve performance with certain settings when it promises to send draw-calls at a fixed interval. Portable devices like laptops that suffer from overheating issues will also benefit from Vsync in many cases since the CPU and GPU will never waste performance on drawing things the monitor won’t benefit from.
That said some will avoid Vsync in order to get the highest framerate possible mainly in an attempt to lower “input lag” especially in fast paced fps games.
Relying on Vsync while programming is generally not a good idea since the player might notice the gameplay “slowing down” when the framerate is getting really low that in turn may effect immersion when time starts stretching. If you are using Physics objects they may also interact differently if it interacts with your logic that depends on the tick rate and not time.
Just something to keep in mind.