What is the point of the "boost" clock?

If I add, say, +45 MHz. via Evga Precision, does that override the boost criteria and force the card to always accept boost mode (plus 45 MHz. more), or how does that work? Am I adding +45 MHz. to the stock speed, the boost speed, or both? Ideally I would like it so I can always hit my target speed of boost plus 45 MHz. regardless if the card is in or out of criteria for boost mode. Is there a way to do that?

http://www.anandtech.com/show/5699/nvidia-geforce-gtx-680-review/4

That should explain it pretty well.

Boost clock is a chance for additional MHz. If you add +45MHz then it doesn't mean it will run at 45MHz higher clock but it unlocks chance for additional clock what later depends from power limit, temps and voltage.
I see it like a really stupid idea and more marketing gimmick than something useful. Boost clocks are usually not high and are not really affecting daily usage but it looks good on the box as higher clock than competition.

When both AMD and Nvidia had no idea how to improve their cards then they added boost clock. Actually most overclockers are disabling boost in BIOS as it's limiting max OC and causes stability issues at higher clocks.

I hate Boost. I liked my GTX 460 1GB which you overclocked manually and it stayed there even in 2D. I set my overclock to 1085MHz on my 2 GTX 760s and it only boosts in games and benchmarks that use more than 60% GPU utilization. And why does it boost by 129MHz instead of 50?

Yup I wasn't a big fan of boost (maybe old fashion) I seemed to have many more stability issues and random down clocks and what not. In the end I ended up flashing a bios (after back up of course ) and currently have a stationary core clock.