After years of using these, I got rid of them. They mess with the midrange and you get varying results, this can vary by cabinet. Speakers boxes are designed to radiate sound and putting them on a sponge affects how the cabinet resonates. I use Event ASP8s which are a large cabinet with an 8 inch speaker and the foam underneath made the mid-range indistinct.
If you have a base or a pair of stands that are resonating with the speaker or in the case of your cabinets being small, then they might make sense because smaller speakers don't tend to resonate as much unless you are overdriving them. De-coupling the speakers from resonant sources is a good thing but for solid stands which are well weighted and absorb low resonance, the foam is not necessary and can even mess with the response of the speakers, my experience anyway.