I think I understand sharding to be putting back your sliced up data (the shards) into an easy to deal with aggregate that makes sense in the context. Is this correct?
Is sharding mostly important in very large scale applications or does it apply to smaller scale ones?
Sharding is a concern if and only if your needs scale past what can be served by a single database server. It's a swell tool if you have shardable data and you have incredibly high scalability and performance requirements. I would guess that in my entire 12 years I've been a software professional, I've encountered one situation that could have benefited from sharding. It's an advanced technique with very limited applicability.
Besides, the future is probably going to be something fun and exciting like a massive object "cloud" that erases all potential performance limitations, right? :)