While I agree with the visual aspect of FPS, you would loose responsiveness if you forced 30 fps. Pages where the webgl context covers the entire window might not be good candidates for this.
Good VR hardware usually does 72 fps (Pixel phones are 90). When a person is moving / rotating their head, 30 is not going to cut it.
The other issue might be sync of animation with a Webaudio context. Webaudio is extremely accurate. The 30 might work better than higher for longer animations, because consistency would be better. In my recent work, I am generating 200-250 animations / minute. As each animation must end on a frame, I need to keep track of any lost time & start animations already in progress as needed. Higher makes this easier.
So, I guess your use might inform your area to optimize.