When the follower falls behind with respect to the leader's body, the force of the connection becomes considerable when she finally acknowledges it. This also does not feel very good to the follower and is entirely of her own doing. Some teachers, including national names, would have you deliberately put weight into your partner. One consequence of complete isolation is a light lead in all circumstances. The cumulative effect of years of moving joints in unnatural ways puts an end to a dancer's career.
More force creates injuries faster and ends one's dancing career quicker.
Thus, in teaching complete isolation, the national names who have to teach this stuff for a living are acting rationally in that they are simply trying to survive for as long as possible. This has a lesson for the rest of us. Leads do not have to be forceful and connection need not be heavy to produce the desired follow. Therefore, since you do not need something that is bad to dance well, don't do it. In other words, lighten-up.