Jump starting (according to haynes)

[827Roverman]

Firstly, Happy New To Everyone, I treated myself for Christmas with a new Haynes Service & Repair manual (my old one was rather dog eared). Today I had a look at it for the first time, I spotted something I thought a little strange (to me anyway) On the section of jump starting from a booster battery, It tells & shows you how to connect the jump leads, all common knowedge so far, But the it goes on to say "Start the engine using the booster battery, and run it at idle speed, Switch on the lights, rear window demister, and heater blower motor, Then disconnect the jump leads in reverse order, Then turn off the lights etc" I have jump started many cars over the years without switching on lights, heater etc, My question is, what is the need, or purpose of doing what Haynes say regarding lights etc ??