Reasons to use ONE fares?
 

OK I am a newbie to these fares. I can understand a nice vacation or if you happen to have a biz meeting in asia then europe then back to the US. as a MR does it make sense? (transoceanic RT is $500 and 10K miles so better miles value).

Also if you fly JFK-NRT (for example) in F it is probably cheaper just to go around the world am I correct?

Anyways what are the other tricks of the trade?

Only one reason to ever use a OWE fare: it is cheaper than the alternatives. You can make EXP on a single AONE5 with careful routing (but not outrageously so); bit better than those 10 trans-Atlantic off-season fares, and a bit more comfortable in A. But if you don't want/need to travel to the cities that you hit on a OWE, then it isn't the best value for a pure MR. The best way to look at OWE is that you get a dozen sectors for the trip you need to take and an extra 8 for more trips (e.g. 3 "free" round-trips in NA if you have the right routing and city pairs); also don't forget the OWE tickets are fully changable, with free date changes, unlike most discounted fares. This gives tremendous flexibility within the rules (again the value of this varies tremendously by circumstance, for me it is critical and worth paying double to get it).

Yes, materially cheaper. And if you are doing HKG-US East Coast, which direction you go makes no difference (roughly equidistant), so going on a OWE RTW instead of RT transpac is the way to go. Cheaper, and you get all kinds of freebie segments thrown in.