FCOM PRO-SUP-70 Power Plant, Manual Engine Start,
"However, manual starting is recommended in the following cases:
• ......
• When expecting a start abort, because of:
• Degraded bleed performance, due to hot conditions, or at a high-altitude airfields.
@McHale, We are talking about choosing (at max motoring N2) when to select the Master switch on our selves whilst using the ENG MAN START pb-sw to open the start valve.