A trading plan to a trader is much like a road map to a traveler. The road map shows a traveler where they are and how to get to where they are going and it gives them an overall trade strategy to follow.Traders with a trading plan are more organized and less emotional.
Yes a wise trading plan is must to succeed in stock market. Traders must always have a trading plan which is best suited for the current market need.
I think that a trade management plan helps a trader to achieve their goals and target. It is more or less very similar to a road map. Its good to have a trading journal too as trading journal can be helpful in evaluating traders mistakes.