Teamwork in martial arts?

I once attended an aikido seminar where one session dealt with techniques for security personnel; in one of them you worked together with another person to restrain a third person and carry them away. It was a simple series of joint locks, but coordinating with a partner added a whole new dimension to it.

On another occasion, during randori practice, I had to defend against two of my seniors; and instead of simply rushing me, they took their time, carefully circled around me, and simultaneously pounced. Aside from entertaining the whole class and proving how I sucked, I think it also highlighted the effectiveness of a coordinated attack and teamwork.

Now, a lot of martial arts teach you how to deal with multiple opponents. But how about working along a partner or partners in dealing with one or more opponents? Is and should it be part of martial arts training?