I recently went from four cones to three under my speaker bases. The bases have three threaded inserts in the back for this reason. I use rounded cones instead of spikes, both of which came with the speakers, because I have soft pine floors and the sharp spike would go right through the wood.
The three cones couple the base to the floor much more effectively by increasing the load on each point, but also because three support points are always self-leveling whereas four points could rock slightly. It is less stable with three than with four because the overall footprint or contact area is smaller, but that does not worry me because the speakers are very heavy. The result is that the bass became more focused and articulate. Extension also increased slightly. I found it to be a very worthwhile improvement which did not cost me anything.
The three cones couple the base to the floor much more effectively by increasing the load on each point, but also because three support points are always self-leveling whereas four points could rock slightly. It is less stable with three than with four because the overall footprint or contact area is smaller, but that does not worry me because the speakers are very heavy. The result is that the bass became more focused and articulate. Extension also increased slightly. I found it to be a very worthwhile improvement which did not cost me anything.