appointments additional price field and adding extra fields

how is the field " Additional Price "

mean to be used ?

if i add something here like £10 ...
this gets added on top of the original ...
but whats the purpose ... client does not know about this extra charge ...

is there a better way of using it ... maybe im missing something here

#2 is there a way to add extra text field for the client to fill ?

#3 will be nice to add a google map at the bottom of the booking to check client - provider distance

thanks