A big part of team cohesion is everybody being on the same page at any given time.

If they are socializing a lot outside of work without you, you will never be in the loop.

In real terms: you will be working on death march projects, your code will be thrown away, you will not be consulted about adopting new techs, etc.

Also: groupthink will be very strong and debate will take place very rarely, leading to hasty decision making and stubborn unwillingness to change.