It is very important to use your Witness votes on Witnesses that you consider are adding value to the Steem Blockchain. In brief a witness is someone who runs a server 24/7 that is responsible for validating and producing blocks on the blockchain. The good thing is everyone has 30 votes to decide who they trust and believe is adding value.
Good Links to Read:
https://steemit.com/steemit-guides/@pfunk/a-full-steemit-user-s-guide-to-steem-witnesses
https://steemit.com/steem/@steemitguide/steemitguide-what-is-a-exactly-is-a-steem-witness-and-why-every-user-should-vote
https://steem.io/steem-whitepaper.pdf
From the Whitepaper:
In the world of cryptocurrencies, the public record is commonly referred to as a blockchain. A block is a
group of signed transactions. With Steem, block production is done in rounds. For each round, 21 witnesses are selected to create and sign blocks of transactions. Twenty (20) of these witnesses are selected by approval voting and one is timeshared by every witness that didn’t make it into the top 20 proportional to their total votes.
The 21 active witnesses are shuffled every round to prevent any one witness from constantly ignoring blocks produced by the same witness placed before. Any witness who misses a block and hasn’t produced in the last 24 hours will be disabled until they update their block signing key.
This process is designed to provide the best reliability while ensuring that everyone has the potential to participate in block production regardless of whether they are popular enough to get voted to the top. People have three options to overcome censorship by the top 20 elected witnesses: patiently wait in line with everyone else not in the top 20, or purchase more SP to improve voting power. Generally speaking, applying censorship is a good way for elected witnesses to lose their job and therefore, it is unlikely to be a real problem on the Steem network.