I use hot stones in almost every massage. I include it as a standard.
(Except prenatal massage or lymphatic drainage, of course, and I take the proper extra precautions, observing all contraindications.) I hardly ever do a stone layout
I don't do a spa-style thing, either. I very often combine hot stones with corrective neuromuscular or deep tissue work, and it really helps, with fascia, trigger points, and knots. Let's just say that since I incorporated the use of stones, the 2-hour sessions are much more popular with clients now AND that length of session no longer wears me out!
I find that hot stones go wonderfully with NMT and deep tissue. Often, it's not the muscle itself that is tight, but the fascial layer above it. Fascia doesn't respond to pressure, so it will not loosen up under deep pressure. If you've ever had a client that you could dig into for hours and still not loosen up (or if you've been on the receiving end of this) then it's not the muscle that's the issue--it's the fascia. Fascia does, however, respond to either a slow sustained stretch (using enough pressure to avoid slippage across the skin and nothing more--and this stretch must be held for 90 seconds at minimum, often longer), OR it also responds to heat. Under either of these techniques, fascia loosens, becoming physically and literally more gel-like. It is only then that you can get into the muscle. Cold stones may feel very good, but they do not produce this effect and will not loosen fascia. If fascia tightness isn't the problem, cold stones are great. Often, though, the culprit IS the fascia.
Hot stones are also great because not only does it do a lot of the work for you (and very quickly) by loosening this fascia, but it also loosens a lot of the muscle as well, allowing you to get twice the work done. It also feels very good to the client--less discomfort and soreness. The heat is very relaxing and soothing. A really nice touch is, for example, to set some large stones on certain super-tight areas (like low back or hamstrings), and massage another area with the stones in your palm, and then switching. That way, you have stationary stones doing some work for you before you even get to an area, and you're massaging another area with your palp stones doing much of THAT work for you too, and then you switch, putting the stones on the area you just worked (or another area, whichever) and then working another area with more palm stones. Veeery efficient
That said, I think cold stones are also an awesome idea, and I am deeply considering (and I'd highly recommend) using cold stones on an area that was deeply worked to soothe the tissues back down and minimize inflammation
Hope that helps
Hugs,
~Jyoti