25% and 75% would sound identical alone, but in a mix there often are interplays where it can create a difference. An easy way to hear it is to run two synced oscillators, say a square and a saw, with sharp attack. The resulting sound should be sufficiently different, one side would dampen the attack compared to the other. Furthermore, I think in hardware synths and those that emulate them changing pulse width can cause the module to implicitly shift the signal up or down to ensure consistent average voltage, further complicating things. I am curious what you mean by compression.
Good point. If I have 2 oscillators, and no control over their phase as they mix, then an option to choose 25% vs 75% for one of them would at least offer some variation instead of none.
As for compression, this [0] is a good intro. Most commonly it is applied to a signal deliberately to achieve a desired outcome, but I'm referring to a (generally) undesired speaker nonlinearity [1] near its maximum power handling capacity.
