"Put simply, a military manouevre to reduce the chances of being shot down whilst on a long straight final"
Funny enough it has an additional purpose these days in heavily impacted areas, noise abatement. A Fighter dragging it in from the initial all dirtied up makes a loud, long footprint. Coast in from the initial from a high altitude at fast speed and you reduce the number of times the duty officer has to pick up the noise abatement hot line.