The basic two-space jump without any other stones close by is a loose connection - the opponent can cut the two stones apart in many ways. The Fujisawa Tesuji Dictionary contains a detailed review of the methods to cut the two space jump. (See Slate and Shell Volume 1 pages 4 and 5.)
The two-space jump is often used, nonetheless, because it is light, quick and there are often supporting stones around. However, it may often be preferable to use a large knight's move instead - it is slightly more strongly connected and also gives a better direction, and can often be almost sente, since it can be used to press the opponent low.