To follow up on mcdhu's post:
For little (FAR23) planes,
Vb is also the speed at which a gust that produces limit structural loads also brings you to the brink of a stall. Above
Vb, a gust can increase alpha, and thus wing lift, until you bend or break things, without stalling. Below
Vb you will stall before exceeding the limit load. This makes
Vb (or less) a safe speed when you might encounter really big gusts. I'll have to go back and read FAR/JAR25 to see if this is the same for the big stuff.
Of course, there is more to safe flying than just avoiding bending things. A stall, especially in turbulence, could lead to a close encounter of the terrain kind. This often exceeds limit loads
.