Dimming stats cost around £40-50. They really are necessary, rather than just using a low wattage bulb.

For example, in the summer time, the ambient temperature rises. If it goes above the temperature set on the thermostat, they bulb will either dim (as it names suggests) or even turn off completely.
If you don't have your bulb on a stat, the temperature will keep rising inside the viv.
During that hot spell we had in June, there were a few occasions where my beardies bulb wasn't even on.

I know that doesn't happen very often, but for piece of mind incase it malfunctions, it really is a necessity.