@jhinsc: If you have a TDI with a known weakness - for example, the BRM engine's cam, which is known to wear, a UOA can indicate whether wear metals are high or not. I was considering doing a pre-emptive cam change, but the low wear metals reassure me that I can hold off until my next timing belt change. Alternately, higher wear metals - particularly iron - may tell someone that their cam's time has come. It allows some (me) to sleep more soundly at night.
It also tells you whether your oil change interval can be extended - which, at the cost of some synthetic oils, will save you money in the long run.
Some people want to know more - and thus, sample new oils to see what's in them... more power to them.