When the waves turn on and you're ready to rip the bag out of it you reach for the performance shortboard. Generally, you'd ride boards in this category in waves between 3 and 6 ft, although that's only a loose guide as wave steepness is also a factor. In the not too distant past many of us were struggling on performance shortboards in slop. But surfers have collectively wised up to the benefits of shorter, wider boards (i.e. summer grovellers & hybrids) in junk surf. But beware of the claims made by producers of these types of surfboards - they won't hold in and give you the control you need when the surf starts to pump. If you don't have one already, you need a performance shortboard in your quiver.
