AKam,
A longer rod lets you cast better
You can move more line for each sweep of the rod, better action for feathers, lures pirks and jigs. it also allows better striking action where required, the more line you can move the faster the hookset.
You have more control over your line, eg on a crowded charter boat you can keep out of the way of tangles easier.
A shorter rod has more leverage against a hard fighting fish thats holding deep and straight down. This can be really hard work on a long rod.
A thru action rod is softer and has a cushioning action, it generally bends all the way down to the handle on a bigger fish. A fast taper is more meaty in the midlle and wont generally bend further than this section.
you need a fast or medium taper if you going to strike at fish like bream where you need to be quick.
hope this helps
Paul J