Exactly - to be clear I don't do this to get a lower fare - it's for convenience and ease of travel as things change quickly in my schedule (and to avoid the massive and inevitable change fees). I frequently have fixed meetings and dates - but in between is still uncertain - and I am in Asia two weeks a month lately. To give you an example - on my upcoming trip this weekend I knew I had to be in Japan on certain dates, but I hadn't pinned down my trip to SIN yet - so I purchased the outside trip first - and then waited a few weeks until my schedule was clear - and then purchased the inside trip.

There is nothing illegal or unethical about it at all - and all flights are UA - and I have NEVER been questioned...