[BillyMac]

Funny that you should ask, it's a NFHS point of emphasis this year:

THREE-SECONDS. When a team is in control of the ball in its frontcourt, a player of that team may not remain in the lane for three seconds. The lane is bounded by the end line and the farther edge of the free-throw line – and includes the lane lines.
A. Team control. In order to understand the administration of the rule, it is necessary to know when team control exists. Team control exists: during player control, holding and dribbling inbounds; during a pass between teammates; during an interrupted dribble. Team control continues until: the ball is in flight during a try for goal; an opponent secures control; the ball becomes dead. Team control does not exist during the tapping of a rebound or when the ball is loose following a try. There is no team control during a throw-in. The three-second restriction is not in effect when there is no team control, and is terminated the instant team control ends.
B. Exception. Allowance is made and the count is momentarily stopped when a restricted player has the ball and dribbles or makes a move to try for goal. However, the previous count is resumed if the player does not continue and try for goal. Some may feel that exception complicates the rule, but it is necessary in order to balance the offense and defense. The most obvious misinterpretation of this rule is when the restricted player has a two-second count when he or she begins the move to try for goal, but is stopped or the ball is batted loose. The player involved, while in the lane, attempts to regain possession and instead of continuing the count, the official erroneously stops it entirely. If the player starts a move to the basket and the ball is jarred loose, the previous count is resumed and results in a violation if it reaches three seconds. The purpose of the rule is circumvented if a violation is not called when this occurs.
C. Screener. Another situation that is occurring more frequently, and which is often not properly called, is when an offensive player sets a screen in the lane and remains there for more than three seconds. The responsible official must make sure that offensive players are not occupying restricted positions for more than the permitted time. The offensive player gains an unwarranted advantage if he or she can “camp out” in the lane, either as a potential shooter or as a screener.
D. Rough post play. When the three-second rule is properly enforced, rough post play is likely reduced. Post defenders cannot be expected to defend and deny an opponent in the lane indefinitely. When an offensive post player “camps out” in the lane, defenders tend to get frustrated and become more physical. Calling this infraction when it occurs goes a long way to decreasing rough post play – an area that has been emphasized for many years.

From the Misunderstood Rules list:
The intent of the three-second rule is to not allow an offensive player to gain an advantage. There is no three-second count between the release of a shot and the control of a rebound, at which time a new count starts. There is no three-second count during a throwin. There is no three-second count while the ball is in the backcourt. There is a three-second count during an interrupted dribble. Allowance shall be made for a player who, having been in the restricted area for less than three seconds, dribbles in or moves immediately to try for goal.

Key points to remember: Advantage, disadvantage. Clean up rough play. And some, but not all, would advocate some preventative officiating, especially early in the game, like, "Get out of the lane".