Why Is Dance Choreography Created?
If they are working with dancers that they are not familiar with, then they must quickly learn of their skills and find a place where their ideas meet with what the dancers can do.
Different dancers have different skills which is why the dancers available will often have a say in what is created by the choreographer. Choreographers will have a very good idea of what can be expected of dancers throughout the country or even the world so many times they can create as their hearts please and then go out and find the right dancers to dance it.
Choreography is usually necessary to create a performance. If there is no choreography or even loose ideas for the dancers to follow, they will be able to what they like and there is unlikely to be any sort of theme or coherency as to what they are doing.
When creating choreography these things need to be accounted for which is why choreography helps to create pieces that are ready for the stage.
Which of these two would you be more confident about seeing a good performance in? Actors acting for 2 hours on stage with no sript whatsoever, or seeing actors performing out a plot that they have rehearsed beforehand and prepared for?
9 times out of 10 what is planned or loosely planned (as in improv) will usually give a better performance. If the dancers are given free will to do whatever they please then in order to maintain audience interest they would need to be extremely versatile dancers, spontaneous, be exceptional skilled, have great chemistry between the dancers...and even then they may not succeed!
So choreography provides a framework where ideas can be presented and performed in a logical manner, that will truly allow the dancers to take the centre of attention, express themselves and showcase their dancing skills simultaneously.
The choreographer understands this and hence creates pieces that utilize the dancers talents to express whatever it is that is in need of being expressed.
They know what to do with choreography to make the most of the advantages choreography offers. Otherwise if they wanted just a scene of dancers that did not require any similarity aomngst them the choreographer could just leave that section unchoreographed and leave it to the dancers.
The choreographer does what he (she) does to express his needs, ideas and feelings as an artist through the bodies of the dancers that he collaborates with.