Thermal reconditioning is a much more gentle process by which to relax and straighten curly hair. Because it is less harsh, it is a good choice for hair that has been chemically overprocessed, or very curly hair. Also, if you intend to relax the curl and color the hair, thermal reconditioning will do less damage than other chemical straighteners.
If your hair has no elasticity left, meaning it breaks instead of stretches, go easy with color, and opt for a semi permanent dye. Do the thermal reconditioning first, then the color for shine.
If it needs it I would recommend you treat your every 2-3 months. Maybe more often, depending on if you bleach, blow dry or straighten your hair a lot.
If your hair is very dry, a hot oil treatment could do wonders. Many hair colors on the market now also have great conditioning qualities which can make dry brittle hair feel soft and silky again. Unless your hair is freshly permed or very oily, this treatment could help.