Everything on Steem is a transaction... every comment, every post, every vote and every transfer needs to be processed.

A witness is a person that has a computer that processes that transaction for us.. and they get paid to do that for us.

Steem cycles through the Top 20 witnesses (based on votes), and then anything left over goes to the person in position 21, then 22, etc...

So, the difference between being position 20 and position 21 can literally add up to hundreds of thousands of dollars annually.

So... since they are making so much money, it's good to know if the person you're voting for is also doing a lot for the Steem platform... are they developing apps or maintaining services? Are they investing in Steem or adding value.

It's important to get it right so make sure you really know who you're voting for.