Picture poker being you vs. everyone else. Now, picture all opponents as everyone else. This "opponent" will have a strategy that while somewhat sporadic, will settle at a mean and balance itself out.

If you are unbalanced versus this "opponent" you will find yourself spots where you don't have value enough, bluffs enough, ect, to where you can be exploited by the average player of our pool. To combat this, you should be balanced in all spots to avoid such.

It a sense, being balanced is much more important if you played all opponents for the rest of time for only one hand. You aren't balanced so Bob doesn't get a soul read on you, you are balanced so you can have the best profit margins in all spots without putting yourself it bad situations.