MarRo

You are fine to book a return and bin the return portion.
 
it depends on who you book through and travel with, but in my (very) extensive travel experience and all sorts of flight related geekery, I have found that in some cases you should not call the airline to cancel the unused return portion - they may reprice you to a one way full fare and chase for the (more than likely significant) difference in fare.
This can and indeed does happen (United scumbag airlines, I am looking at you).
 
 

Our Visa was approved today! When booking the ticket to travel from Europe to the United States a round trip ticket is significantly less expensive than a one way ticket. Is it okay to book a round-trip ticket "just in case" for the unlikely event he would have to use it the return portion? I know throwaway ticketing can result in a fee if you have done this in the past but we have not. I would love input on the subject.

Our Visa was approved today! When booking the ticket to travel from Europe to the United States a round trip ticket is significantly less expensive than a one way ticket. Is it okay to book a round-trip ticket "just in case" for the unlikely event he would have to use it the return portion? I know throwaway ticketing can result in a fee if you have done this in the past but we have not. I would love input on the subject.

I travel quite a bit (and have changed travel plans quite a lot)....so you can book the round trip ticket and after you are here credit the remainder of the ticket to a different trip within the US (and if you find a sympathetic booking agent/supervisor.....they can change the  $175 to  $300 fee). The standard is that you must travel within the year  (if you change the ticket)

The return ticket is fine. Be sure to cancel (or change if possible) it after arrival in the US so they don't mistakenly think you left the US and abandoned AOS. It's quite uncommon, but it wouldn't be the first time I've seen somebody saying it happened to them here.