What is the advantage in knowing the fastest winning sequence if I can win with few more moves than fastest sequence? I am studying from Lazlo Polgar's "Chess: 5334 Problems, Combinations, and Games", there are positions with heavy material imbalance for example like a lone King against Queen, 2 Knights and King under the category to find mate in 2 or 3 moves.

Some of them are not easy for me even after few minutes to find mate with the given 2 or 3 moves but I can easily do in 4 or 5 moves.

In cases like this with large material imbalance why should I spend my energy and time in finding the fastest sequence if I can do the same with slightly more number of moves?
What do I gain by knowing the fastest sequence?
There is no advantage if your goal is to improve your OTB rating.   The time wasted solving a problem in fewer moves would be better spent learning things that you could use in your games.