The spikes allow the speaker to be 'anchored' to the floor for a more stable/solid footing and I would guess help to transfer the vibrations/case resonance to the ground.

I used the rubber feet, it just feels more stable to me this way.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70