i think its called 'automatic sequence' when the sides are paired 1/4 and 2/3, vs 'manual sequence' when its 1/2 and 3/4
I always thought it was for the benefit of US radio stations, back when they'd play entire albums uninterrupted. Side 1 & 2 on separate turntables, then to a station break or something, then sides 3 & 4. A friend of mine has a double-vinyl radio promo of "Music Of My Mind", which is playable only on one side of each piece. I assumed that, for a while anyway, double albums were mastered with a similar function in mind.