The real question in terms of benefit/risk IMHO is which is a greater threat: That your broker will trade against you in such a way to force a SL and/or prevent a TP? Or that your computer, internet connection, power source, EA, or even MT4 crashes -- preventing your hidden order(s) from executing at all and thus your trades go on unmanaged either toward astronomical profits or, more likely, into a margin call?

I may be naive. While I'm sure there are a few bad brokers out there, legitimate ones are far more interested in treating their clients fairly. They want to generate more revenue through more trades/volume (via the spread) than by trying to force investors out of their positions and onto other brokers or out of FOREX investing entiirely.