RE: Essential Guide to Becoming a Steem Witness

In the post OP mentioned:

"First WHATEVER YOU DO, DO NOT ADD YOUR WITNESS TO THE MINER!!!"

Can someone explain this to me in a little more detail. Does this mean I should have different accounts for the witness and miner at all times, or is it okay to have a witness and miner sharing the same account on one instance? Just a little confused by this. I'm currently running miners on multiple instances, but I am using a different account for each instance. Each instance does have the same witness name and miner name though. Is this incorrectly set up? Thanks in advance for clarification!