Being double weighted is supposed to be a cardinal sin in T'ai Chi.
Don't have the weight equally divided over both feet, we are told.
You can read amazing debates on internet forums about this topic, where people quote chinese words, theory and phrases from books. I rarely see anything from a personal standpoint.
I think it's pretty simple. Don't get caught flat footed. You can have your weight equally distributed on both feet but the mind / intent needs to be single focused. Furthermore the mind must not be rigidly fixed becuase ultimately it is a double weighted mind that gets caught.
Read Takuans' "Unfettered Mind" for a better explanation.