For Certain Situations
The Z-Lite sol is a nice pad for several different situations. If you're going ultralight and really want to shave some weight you may be able to get a comfortable nights sleep out of either the (S) or (Reg). If you're accustomed to the 3.5" Q-Core from Big Agnes you will not get a good night's sleep using this as a stand alone.
The best use of this would come from a doubling act where you might use this to enhance the insulating values of another pad. This use might give you more warmth for weight than buying a cold weather pad (or at least for cost)
The downside to the SOL is that while light, it is bulky. Lashed to the outside of a pack it will perform well but it takes up far too much space inside a bag.