I got asked that question a couple of months back and wrote up a whole post on it. The link is at the bottom.

As a quick update to that post I'd say three reasons for giving busy a go are:

• Constant user interface improvements: At the time I wrote the original post I found the vote slider really useful (as it wasn't available on Steemit when I was below 500SP) now I use the vote breakdown a lot (you can just hover over the thumbs upvote symbol and see which generous people have added to your payout and how much). Busy also shows your current voting power, vote value, and the steem and SBD prices. There's lots of info to save trawling through steemd so much.
• Free upvote (it's at a lower level now and it does depend on the voting power of your followers but still, it's free!)
• Ability to bookmark posts and resteem posts older than seven days old.

There are probably other things that other people also find useful. It's worth having a look just to see what you think!

https://steemit.com/utopian-io/@miniature-tiger/busy-busy-busy-org