its not illegal unless you are doing it for purposes of 'manipulation' and tax evasion. but really the illegal activity is in accounting, not the trading itself.
useless unless you have some multi time frame system that scalps on minute bars and does longer term positions on other length (more minutes, hours, days, weeks/etc) bars. realistically? lets say you are short a long term position on a stock, but want to trade in and out of it when you see an opportunity (ie you are short amazon, but the signals all point to buy in the very short term). Then it makes more sense.
work it out on paper. trying the long term on one account and the short term on another account works out to the EXACT same as trying both on a single account (exiting and reentering the 'long' position at a better price a based on the short term signal). there is no magic here.
i use trade navigator and it has it problems but one thing I like is that you can view your auto trade positions separately from your manually traded positions. If you have a couple different positions created from auto traded programs you can trade them as well.
agreed. i wasn't referring to seperating accounts (which only might serve an organization point). just referring to it being valid to be 'long and short' (neutral) on the same position at times. on the other hand.... lets say you are long aapl for a long term trade in your investment account... but in your trader status account, you are in and out scalping it. That seperation serves a tax benefit too.