In 6v6 we have a meta game to have alternatives and locked classes based on our skills and the map that is chosen to play on unlike the highlander. In some maps and situations certain classes are very effective that would help the team in very different ways.
Maps commonly played in 6v6[edit]

These are all the maps trhat are played in 6v6!
Attack/Defend
cp_gravelpit

Control Points (5)
cp_badlands
cp_granary
cp_granary_pro
cp_gullywash_final1
cp_metalworks_rc7
cp_process_final
cp_snakewater_final1
cp_sunshine_rc8

King of the Hill
koth_viaduct_pro7



For an example in the 6v6 map called Snakewater a sniper could be really affective and also in a map called product due to the hight advantage a sniper has in these maps. In the map Sunshine a sniper could get a lot of headshots due to the angles the map has.

A another example would be for engineer in the map called Gravelpit. Engi could defend the last point of the Gravelpit very easly due to the extended hight advantage he have for his sentry.

A spy in procces or Gully Wash could help his team to drop the enemies uber due to the close corners he has to headshot a enemy and run away silently or even trickstab them.

When pushing in the map Granary a heavy could be a really good class to take down enemy players in numbers.

Now let's talk about the locked classes that must be in a comp match of 6v6.
1 agreessive scout
1 roamer soilder
1 demoman
and 1 medic.

These are the classes we definately need and they can't be switched.
So it depends on the map we play on and the situation but it more matters on the skill of indivisuals. If nobody in our team is good at sniper or spy than we can't let our team down just by using another class space.

Listen guys we could only 2 different utilites (spy,sniper,heavy or engi) when playing in 6v6 and it depends on the situation, map and the skills of indivusuals. So make them count.

We are going to have discussion in the comment section about it!