Additionally to coopers comment and why I also am going to start doing it, it also mimics the natural color of light cycle throughout the day better. The Kelvin scale is what's used to describe a lights color
Sunrise and sunset have a Kelvin level of 2000-3000. The noon sun comes in around 5000-5400k. Since most basking bulbs provide a warmer colored light (usually in the 3k range) and our tube uvb bulbs provide a blue light (usually in the 5k+ range) it's more natural to start the day with just the warm colored bulb, then to turn on the bulb that provides around 5k, and then to end the day again with a sunset mimicking 3k kelvin. Thats in addition to trying to more mimic that natural cycle of uv exposure.
I think cooper would agree none of that is necessary for our dragons, its more of a why not type of thing.
-Brandon