During development of the game [Prototype] I experimented with a number of game logic update scenarios, including variable timesteps, fixed (potentially multiple per frame) and limited fixed (potentially leading to slow motion), in combination with factors like enabling and disabling vsync, taking into account camera movement (speed, mostly horizontal or mostly vertical?), amount of explosions and debris going off, etc. To try and find the best experience for the player at each moment.

But we always had physics running at a fixed update rate (always receiving a constant delta time) regardless of any of the above. Trying variable rates there will ruin the stability of your movement, collisions, platforming, etc in any system that is complex or requires precision and predictability.