Changing partners

When I teach, I make sure that everyone swaps partners and make also sure that people that came with their partner get to pair up every two or three exercises. I am very often asked why do we have to swap partners.
Unlike most ballroom dances, which are aimed for competitions and choregraphies, tango is improvisational. As such, it is important that one man can dance with any woman. It's important that he can make her understand his energy but, even more important, that HE understands how HER energy will receive his marks. If I dance with 100 women I will find that to do a single step I have to do it 100 times differently. All of this because in tango we're all different (sorry for those of you who copycat your idols! The true must hurt!) and we all have different energies that we have to understand.
Furthermore, dancing always with the same person will allow for accommodation and loss of that capacity to adapt to your partner.