Sometimes it's better to kick for 3 points than push for the try. Everybody loves to score tries, but are they more important than a win? Good times to try for a drop-goal or kick for posts are to get the first points on the board, to gain the lead just before half time and of course to sneak a win if just trailing at the end of the game.
Remember your opportunity to score might not come again!
Remember that rugby is a game where big leads can be whittled down by good patient play. Kick for goal, get the easy points and slowly claw your way back into the game. The moment you are within 7 points of the opposition it is game on - your opponent is back under pressure to defend.
This tactic will of course depend on the situation, as sometimes a try might be the only way to win the game!