Depends on the beach - if you were fishing Whitley Bay you'd be casting over the fish at 90 yards! 30-40 yards is about all you need there. Similarly at Blyth you'll often catch fish almost at your feet; so many times I've seen lads blow there reels up and dump their baits no more than 20 or 30 yards, then when they've unpicked the birdie they find a fish has taken their bait. Mind you there are also beaches where the further you can chuck, the better your chances - it really depends on the location & lie of the beach.
Gary