Length in dummy can be valuable if we ruff out the suit, but length and strength in dummy can used in a variety of ways to produce extra winners.
One place that we do not need a jump bid to show a weak hand is in the passout (PO) seat, also known as the balancing seat. In this seat with a weak hand, say 5-8 HCP, and a long suit, we would not bid; we would simply pass the hand out. Bidding here with so few HCP may give the opponents a chance to reach a better partscore or game that they may not otherwise reach. Since we will not bid in the PO seat with a weak hand and we could make a simple overcall with 9-10 HCP and a long suit, then a Jump Overcall in the PO seat is free to be used to describe a different type of hand that can otherwise be difficult to show.
A balancing 1NT bid can be a wide-ranging action, about 11-15/16 points. This 5-point range is much larger than most Notrump bids and leaves partner with a more difficult bidding situation. Range Stayman is a tool that can help Advancer better determine the values of our hand and if game is a possibility.
There are certain auctions where we have made a bid that has “fully described our hand” and we leave the bidding up to partner. In auctions like these, for example when we have opened the bidding with a preempt at the 2-level or 3-level, then we usually are not very sure of what partner has for their bid and we want to leave any further decisions up to them. But sometimes we have more shape than partner expects or our instincts tell us that is right to bid on. When that is the case we do NOT want to just take over and bid again – we told partner we would not bid anymore after our first bid. In an auction like this we can use a Double as a conventional bid saying “I want to bid more”. This is called an I Want to bid Double and it applies in very specific situations