story
If you're using the majority of Modernizr tests it makes sense to use the full library, but for the most part me and the other devs I've talked to usually drop the whole library in for ease of maintenance, but mainly use it for one feature alone: touchscreen detection.
Lately I've tried putting some of my HTML on a diet by replacing my need for Modernizr for the purpose of touschreen detection with this snippet:
if(('ontouchstart' in window)||(navigator.msMaxTouchPoints>0)){
// code for touchscreens here…
}
This keeps the test and the result together in the code, and eliminates the need for a library, which can also be an additional single-point-of-failure outside of your control, especially if hosted by a CDN.