This is a matter of opinion and situation. Ill give you some positives and negatives
-Positives
-It gives you something to do late in the game
-You get a very strong Pokemon in the end
-some wifi/competitive battles are held at level 100
-makes the game easy
-Negatives
-unless your Pokemon has a competive moveset, it's still won't do well in competive battles
-it will require a good amount of work to get your Pokemon to level 100
So, in summary, if you really want a strong Pokemon and desire an activity to do late game, train that metal penguin to level 100
