why do people call a skinny neck fast?

[BlueTalon]

As others have mentioned, what makes a neck "fast" has more to do with than just size. I like jazz necks. But I got a bubinga jazz neck from Warmoth, and I could literally play faster than I previously could on maple jazz necks. The wood allowed my hand to move with less resistance. Would unfinished maple necks have had the same effect? I don't know, but I'm a firm believer in the reality of fast necks based on my own experience.

 

[twc1313]

I've started to notice that a flatter radius equals easier playing for me and neck thickness isn't as much of a factor.

One example is a 7.25" radius jazz neck would give me fits, whereas a 12" radius P neck felt like I could pull off harder parts more cleanly on it.