adjustable backstay on a masthead sloop why?

[dockmaster]

Now I am confused went to look at probable new boat today and found no babystay !! only forestay adjustable backstay 2 shrouds and 4 lowers ??

 

[sailorman]

forward lowers do same job

 

[dockmaster]

so dont bother adjusting the lowers just the backstay.

 

[sailorman]

In one