Excellent for: 1. Transition from demo to live, so now you can go demo > MICROS> large contracts 2. For traders who like scaling in and out 3. testing new strategies 4. Long term positions 5. If you really hate stops, you can take opposite positions to lets say short 1 ES with long 5 MICRO ES at one level and manage the trade that way. ( I personally think you are wither right or wrong but I have seen traders use this and for some it works)
Yes, you can be long the ES and be short the MES and that is legit and fine with exchanges, brokers and regulators.
"Can you go long and short really?" He would have known this long ago if he never had me on ignore. He'd even know that you can be long and short in the same contract month in the grey area, as a retail trader. But he's a moron who ignores people who he does not understand.