@ the OP
Corvettes are great for quickly fighting for dominance over neutrals on the maps, and I consider this their primary purpose. If they send flak to defend, just send light frigates in as well
. Corvettes even out your early game fleet capability.
Corvettes are also a great way to support your fleet if its a close battle and every ship counts. You spam some quick corvettes to get to the battlefield earlier then your opponents reinforcements and you have a great way to turn the tide before his reinforcements get there.
Also, corvettes make great player distractions, using them to tie up your opponents moves/second and force them to player harder by opening up multiple fronts.
The faction that really got the short end of the stick is Vasari, who have pathetic light frigates and corvettes....if it weren't for the Orky and grabbing neutrals the Vasari actually would have an almost unplayable early game on cramped maps....
Hmm, i'd say that vasari have the best light frigates, as long as you upgrade them to get self healing. Combined with a vasari carrier's healing ability and some early armor upgrades, you have yourself a good early fleet.
Most vasari players don't play this way because they have many more tried and true orkulus spam techniques that far outweigh the benefits of getting a strong early fleet.