Not childhood "sweetheart" but childhood grate frend and co-conspirator of mischief - knew each other all through up to university (always just as mates), then spent a proper growing-up decade out of touch, met again when I asked him to my 30th.
Advantages: (i) families are friends; we all get along & always have (ii) I remember girlfriends of dh's that appear to have slipped his memory = no surprises, no baggage (iii) no doubts about what he's really like, as qualities consistent throughout (good things: loyalty, friendliness, brains, go-getter nature; less good: megalomania) (iv) as he's always known me, presumably he has the same sense of my qualities so has made an eyes-open choice & actually really likes me
Disadvantages: there was a bit of weirdy competition over the grandchildren at first. Imagine having a granddaughter who takes after, not your family, but your own best friend - which is effectively what they each had to deal with. Surreal & a bit disorienting. However, this has been lived through & all is fine.