Whereever it is not possible or not advisable to band (which is the majority of areas) this method is the only one which can be practically applied by almost every ornithologist or observer who is willing to spend the time getting familiar with a different kind of equipment and a different method of observation one is used to.
In research projects where a continuous and dense banding is in place, acoustic monitoring is an excellent additional tool and provides information not accessible by visual observation of the banded birds. It has the advantage that the cranes to not need to be disturbed at all, it is even not necessary to see them (and it is preferred not to be seen by them).
A long term monitoring of cranes leading to detailed indidual life history facts is possible even if no banding is in place. Cranes are much more flexible as one would conclude from just visual observations. They change their territories (around 40% of the territories in a given area are occupied by a different pair than in the previous year) and partner (around 25% of the crane pairs divorce or get a new partner during their life) to a surprisingly high degree.