What's the benifits of both? I see the pros pitching lots of plastics and jigs but what determines what to use? What's the benifits and cons of each?

The difference would first be appearance. Jig usually will present a bigger/bulkier bait from the skirts flaring out. The second would be that plastics can make their way through thick cover much easier than a skirted jig will.  Jigs (IMO) are better for rockier structure and plastics are better for thicker/more vegetation situations. Hope that helps some. 

The biggest factor is finding out what the fish want on a particular day. I almost always start with a jig and then move to plastics if i'm not having luck. This is mostly a confidence thing, but also I find that the quality of fish increases when using a jig while the quantity increases when using plastics. Not to say you won't catch a few small ones on a jig or that you cannot catch big fish on plastics because that is far from the case, but in general this is what i have found. 

 

The only time I key in on plastics and keep the jig on the deck is if i'm punching grass mats or there is a lot of "clingy" weeds on the bottom. The t-rig plastic will slide through thick cover better than a jig and not get hung up as much. 

^^ what he said.

 

I generally start with a jig tied on, beacuse IMO it's more versatile - it can be dead sticked, hopped, swam whatever you want.  If I find them in weedy/grassy areas where a plastic will slip through easier I make the switch / if they want it swimming I'll switch to a swim jig or something similar etc.  

 

This allows to try to target the bigger fish in the area with the bulkier profile first too.

Personally I like jigs better in these situations and in no particular order or combination......cold water, dirty water, hard cover, deep water, and in the fall. When I tend to use plastics more, also in no particular order or combination, is in clear water, warm water, heavy grass, shallow water, and behind a guy fishing a jig. But there are times when I prefer one or the other, but the fish tell me other wise. I don't try to argue with them, I usually have a jig, and several plastic presentations rigged up at all times, unless they are obviously biting one much better than the other.