[unconed]

If the shots weren't timed to a regular fixed clock, then there would be visual jitter in the pattern. Even if you correctly spawn shots in between two ticks, each bullet would only first appear some random distance along its trajectory.

If an enemy spawns e.g. a circle of bullets, you would see it rapidly expanding/contracting.

I suspect a variable frame rate bullet hell game would be harder to play, but I'm not a fan of the genre.

[eru]

You could probably make a difference between physics frames and visual frames?

Games like Quake 3 do that, I think.