I think the of combination heat and age is what causes the plastic on those sensors to fall apart. I took the ones on my 91 Z off, and will be doing the same on my 93 when ever a tire change is needed. It's always best to check the air pressure before drive. As far as I'm concerned, those sensors are useless. If you're serious about keeping the right pressure at all times, nothing beats a pressure gauge.
For those that don't drive much. Keeping the proper pressure at all times helps the tires from developing a flat spot, which is something you want to avoid, especially if you get into the triple digits every now and then.