I use it periodically, even as a blessed UA
Premier member... lol.
If I find an itinerary that I absolutely have to have, exactly the way I want it, but am not quite ready to buy it, I'll go ahead and use fare lock.
Examples of this include waiting for family members to commit to a trip. I have to have them booked on the same itinerary as myself (which wasn't an intuitive one, so it took a lot of work), but they weren't ready to buy it at that exact moment. So, twenty dollars later, I've bought them an extra week. I was glad; the fare went up by $400 before they were ready to pull the trigger.
Also, vacation planning when work is slow to approve LOA, just like your present situation.
Most of the time, I have no use for it... but once in a while, it comes in very handy.