.30 and .3 is the same number, by the way.
I don't use them, never have and probably never will. I see nothing wrong with them unless you have a lot of filter feeders in the system. SPS are filter feeders too. A 100 micron sock starts out as 100 microns but as it fills with stuff it filters out finer and finer particles. As far as stuff collecting in the sump, that is what I want as it makes it easier to suck out with my Python. When I feel the need to polish the water, a Magnum with floss works just fine.
Obviously you can have a great SPS tank and run filter socks or you can have a great SPS tank without them.