My cases are often formant like sounds, which I try to generate. If I modulate two filters independently, very unique and interesting sounds can evolve.
For the bass case I would say, we have VCO --> F1 --> F2. If the timing is not right, the resonance of F2 might just not find enough spectrum to emphasize. And the direction of modulating F1 and F2 vs the spectrum might sometimes be better, if F1(+) and F2(-) are working antiparallel, if this makes any sense.