Standard booster meter VS Boost

Standard booster meter VS Boost Overflow???
Please help!
What is the specific difference between how the normal boost meter and the meter with Boost Overflow works? Below is the info I was given on boost overflow but i don't understand how its any different to the standard booster meter.

Boost Overflow: Lets your boost meter bar continue filling towards the next boost. Boost Overflow will not fill the bar past the limit of 3 boosts.