As well as mixing Assembly into BASIC, BBC BASIC allowed you to use its internal routines from Assembly. You could, for instance, use the floating point routines.
So the BASIC ROM was not a lost 16KB of address space if you were only using Assembly.
Aye. The graphics primitives, and just about everything else, too. A lot of thought went into making those machines conveniently programmable which made them great for both learning and tinkering.
Though the main two reasons I had for assembly were faster maths loops and graphics (via direct access to screen memory including, on the Master, the shadow screen for double-buffered drawing), so neither of those parts where sometime I called much.
So the BASIC ROM was not a lost 16KB of address space if you were only using Assembly.