THE Limit Bid is one of the pillars of the Acol system. It conveys in one bid information about both strength and distribution.
Most natural no-trump bids are limit bids; conversely, most natural suit bids are unlimited. Today’s deal features an exception: the Limit Raise. When you have four-card support for partner’s major you can limit your strength by raising, and this is almost always the right thing to do
An opening bid of 1H is not very informative: it announces opening strength but not enough for a strong opener such as 2NT or 2C; it promises at least four hearts in a hand that is either unbalanced, or, if balanced, outside your range for opening 1NT. This South hand is just one of many that opens 1H. Many a North responds 1S, telling partner about the best feature of his hand, but such a choice displays a lack of foresight. After 1H-1S-1NT what should North rebid? His failure to make an immediate Limit Raise will persuade partner that he has fewer than four hearts. A jump to 3H suggests three-card support only. To play in hearts North must rebid 4H at some point, and partner will ask: with four hearts why did he not raise immediately? The only logical answer is that his hand was too strong for an immediate raise to 4H … and South may be tempted to look for higher things.
Whenever raising partner is an option – raise him. The 3H Limit Raise simplifies the auction and allows partner to devote his energy to the play.