Source: http://www.pittsburghbridge.org/JimmySez.htm
Playing at a trump contract usually will produce more tricks because of the power of the small trumps. When partner opens in no-trump and you have a weak hand with a singleton club and no five card major, it is useful to try to find a suitable trump suit so that partner can maintain communication with both his hand and dummy. The Stayman convention is often used for this purpose. Look at some of the hands you might hold where this might be valuable. I’ll list a few.
(1) Jxxx Jxxx Jxxx x
(2) xxx Jxxx Qxxxx x
(3) Jxxxx xxxx x xxx
(4) Qxx Jxxxx Qxxx x
[box type=”alert”]All of these hands above will play better in a suit opposite a no-trump opener. [/box]
Here is a hand I held last week. I sat South and partner opened 1NT.
Lead: 
10
Notice that by using the Stayman convention we can safely play in either of three suits. If spades had been the rebid we would be playing in a 4-3 fit. This would still be superior to playing in the 1NT contract. The final 2
contract was easily made on this board for a better than average result. This use of the convention is known commonly as Garbage Stayman.