The large size and odd shape of CC
allows uneaten food and other waste to settle into it and out the water column. It also prevents most types of good detritus eaters from getting to it easily. The detritus will then rot in the tank and give you bad water. If you want to keep the CC
you'll need to vacuum it pretty often to keep this in check. If you decide to change it out go with arogonite sand (southdown brand) or playsand (any as long as its "playsand") if you can't get arogonite. Going with a sandbed will keep large pieces of detritus from settling, will be a great filter by itself, and allow all the good little critters move around and live happily. I can't think of any real cons.
For some reason CC
is what's recomended to people new to the hobby by the "experienced" staff of their lfs
, along with the very expensive wet/dry or canister filters. Its also one of the first changes lots of folks do to their tanks. Some folks continue to use CC
for years and are happy with it, but it will be more maintenance.