((Yes, but if the object was large enough it wouldn't matter, the impact would still send up just as much dust into the atmosphere and cause a sun-blocking extinction event. And even if the object WASN'T that horribly huge, its still pretty situational as to whether hitting a larger area softer is better then hitting a single one harder. I.E. it depends upon population centers near impact zones and whatnot. With a single large impact you can at least calculate who you need to evacuate pretty easily.
((I would argue that, at least with asteroids that wouldn't be planetary catastrophes beforehand, spreading it out would be good; a heat wave followed by a cold snap and a bunch of dust in the air are pretty negligible, while a concentrated hit could easily wipe a nearby city or a bunch of farms or something off the map.))
No matter what, the point is, its hitting with exactly the same force no matter how many pieces its in. So if you were expecting an Earth-Shattering-Kaboom before smashies, you can still expect the same boom. Just in a lot of places at once.))
((Hm...I'd say that depends on the exact mechanics of the kaboom and how close to the minimum kaboomy energy the impact was. Imagine four half-eggshells and a book: If you rest the book's weight on the eggshells, they'll probably hold, but if you balance the book's weight on four pins beforehand they probably won't. Okay, that's a terrible analogy, but you get my point, which is: "Explain to be how the planet would blow up from the asteroid impact, and I'll let you know if I think blowing it up might mitigate the damage to the 're-terraformable' level."))
((Really, a not-entirely-accurate-but-still-pretty-good saying I've heard is that if you fragment an impactor like that, you're basically replacing a shotgun slug with birdshot of the equivalent mass))
((Excellent analogy. Or close enough. Really, it depends on the level of fragmentation.))