Frequently when looking at models in medium resolution maps (~4-5 Å), it is valuable to view the C-alpha trace when assessing model map fit (or making figures to show such). 

At slightly higher resolution, where side chains are obvious but backbone torsions cannot be modeled based on the map alone, representing the C-alpha trace with sidechains displayed is often desirable (examples of both attached).

It looks like there is space in the upper toolbar for additional buttons - perhaps adding a button for a Calpha trace representation (equivalent would be P for nuclei acids) and one for a Calpha+sidechain/base representation may be worth considering? (I’m also not convinced of the value of the random atom colors representation as a shortcut, but maybe there is a use case I’m missing?)

Cheers

Oli