Obviously not everyone can be a leader, it's too confusing if we all started trying to lead and nobody followed - and humans certainly survive and proliferate better by working together, which is why the group behaviour in humans has evolved and is so strong among us. A cohesive group with a leader to direct it is more efficient than a collection of leaders and no followers, or a collection of people who just want to go their own ways. So a certain amount of a group or population will usually be happy to conform and get on with their lives within the bounds of that conformity.
And... it would also be beneficial in survival terms for a small % of any population to turn out to be 'leader material' as well, people who are not happy to conform and prefer to galvanise others to their cause, and yet another small number to be 'lone wolves', people who survive on their own and don't necessarily need a group or a leader to survive.
So... that's why a lot of people tend to follow trends, including teenagers, because most of them will be highly influenced by what the rest of the conforming group is doing, and yet a smaller number are 'different', non-conformists, but always present. Because it makes logical sense for our species to contain a strong conformist streak as opposed to a chaotic one, but also to retain a certain number of individuals that will not conform, just in case conformity turns out to be detrimental in some instances. In such instances, the non-conformists may be more likely to survive, and the human race increases its overall chances of survival by always keeping a few non-conformists around.
So in this sense it would be bad for everyone to be a non-conformist, but it is good to always have a few in there.