I’m buying some new reels for my carp fishing and I know a few people who have big pits and they say that they are excellent. What are they actually better at though? What are the advantages and disadvantages of them over normal reels? And why do the spools need so much line on them?
Also, does anyone know if Wychwood riot’s and Daiwa Crosscasts are any good?

Big pit reels have very large spools that contain large amounts of line. That means you can cast a long distance without affecting the depth of line on the spool as much as with other reels. Line peels of a well filled high capacity reel on the cast much better than it does off a half empty one because there is less friction, so the result is that you can cast further.

That is the main benefit of a big pit reel. Against them is that the out-and-out casting reels often lack other refinements, such as a baitcrunner option and sometimes even a clutch (you have to backwind with them instead). Think of them a bit like a racing bike that has been cut down for racing, but would be rubbish for commuter riding.

So, if you are going to be doing a LOT of really long distance casting (distances like100 yards) a big pit reel is a good idea. In reality though, most venues are a lot smaller than that, and people who cast really long distances in smaller venues inevitably end up in trouble with other anglers who don’t expect people to be casting over their lines or in front of them into their swim (especially when most people know that you can usually catch big fish perfectly successfully at your feet). If you aren’t going to be doing enough long distance casting a sensible compromise is a high capacity "standard" reel, like a Shimano baitrunner. The higher the serial number on those, the higher the spool capacity, so a Baitrunner 6000 has a smaller spool than an 8000, while a 10000 would be bigger still. My best guess is that you would want to go with an 8000 or a 10000. That would give you a reel that is good for long distance casting, but is also a great reel for fishing on a shorter cast.