What are the floors like under the carpet? If they are nice finished wood floor that you might want to show off at sometime in the future. Then you might not want to use Spikes. But it the Sub-floors under the carpet are just rough unfinished sub-floor, then you certainly do want to use Spikes.
The problem with carpet is that is is not very stable. Put a speaker or speaker and stand on a carpet and give it a wiggle. It is very unstable. You want the speaker solid. Any movement in the cabinet is a loss of movement to the speaker drivers, and that is not good for sound.
So, to answer you question, Yes, the Spike are for both leveling and Stability.
Prior to this, I don't believe you actually mentioned the type of floor you had. I do have a video I was going to post, but it is for Wood Floors. Still worth a look. This is an AV-Land review of the Dali Zensor 5. Notice when the camera moves to the speaker in the corner, the speakers is spiked to a black granite 'chopping board' -
I'm not sure if they have covered the bottom of the board, but likely the bottom is finished as smooth as the top, so scratching would be kept to a minimum.
I have heard of people using the 'chopping boards' on carpet, it spreads the weight of the speaker base over a broader area, and that can make a more stable base. But, for best result, Spike the speaker into the carpet. It might seem unstable at first, but in time the spike will penetrate to the wood floor below, and hold the speakers stable.
On a very very side tangent, I've discovered a pretty effective way of moving speaker that are spiked to carpet, just one requirement, you have to be wearing shoes. Tilt the speaker back and push your foot under the bottom, then tilt the speaker forward so you foot is supporting it. Then you can slowly 'walk' the speaker to a new locations and to the reverse to get your foot out from under.
This might sound stupid, but I broke the pins on my grill cloth trying to move the speaker by given it a bear-hug and trying to pick it up. From my experience, this is the safest way to move a speaker, even over moderately long distance, especially if you are trying to move it alone. Any type of grabbing or dragging is just too dangerous.
That's probably way more information than you wanted or needed, but none the less, there it is.
Steve/bluewizard