Amusician would use a metronome in practice to improve their performance of which element of music?

Rythm and inner tempo.

Explanation: A metronome is an apparatus that makes an equidistant sound, which is used by musicians to keep the tempo when they are playing. Where each sound of the metronome can be used as one "beat" of the piece that they are playing.  

So the metronome is used to improve the rhythm of the musician, and also there are a lot of musicians that practice with a metronome with the objective to develop an "inner tempo", this means to reach the point where they do not need to use a metronome to keep the beat because they can do it for themself.

i do agree with robert moses’ statements about wiping out cities that are an “impediment to new growth”. in order to have a positive community, the city must continue to grow either in terms of size or economics. therefore wiping out cities that restrict growth benefits the overall society and all the people living in it. similar to a social contract, i believe that if a person was to live in a community they must sacrifice some of their rights, in this case property, for the overall good of the people. as long as these people living in the cities are reimbursed and the purpose of wiping out the cities is to serve the public, there is no problem with robert moses’ core idea.