How is Harmony differnt

[High prince of geeks he/him]

Before Sazed combined the shards neither one was able to due much because of how they opposed each other, leaving things at a near stand still (Preservation). Now as harmony it is mentioned how it is hard for him to intercede. My question is how this is different then just letting two random people pick up the shards, sure they wouldn't have been able to piece the world together again like sazed did, but otherwise everything is the same, besides a few changes to the magic's

[Tempus]

Well, first off, there is the piecing the whole world together thing. Slightly important, maybe a little more credit to making the planet not covered in ash and cruelly oppressed by a god-like dictator? Secondly, Ruin is stronger than Preservation at the moment - two new holders would engender a similar circumstance as before, except possibly this time the new Preservation wouldn't think up a good trick before the world was destroyed repeatedly. Also slightly important, not being a hairsbreadth away from divine destruction. I'd much prefer a god who does not do too much like Sazed than say, a Ruinous god hellbent on slowly destroying everything on the planet only to build it up and destroy it all again.

[Pathfinder]

Also Words of Brandon have said Sazed is starting to get the hang of handling two shards. It is difficult, but that doesn't mean Sazed won't learn how to take a more active role. Then again this is assuming he WANTS to take a more active role. He is a "god" that doesn't want to be worshiped, and grew up in a society that suffered from a perceived "god" that controlled too much. 

[Shardmancer he/him]

Sazed is very powerful.. If he was Odium wouldnt be so scared of him. Acting in small ways of worldy interference are beyond him at this point anyway. But perhaps using both shards intent like Ruining Odium to Preserve Society would be right up Harmony's alley