The other issue involved in "personal use" is "reasonable." This is also sticky and very variable. It is purposely left vague because of the variability of situations but that causes the problem of interpretation. "Reasonable" is in the eye of the beholder, so to speak, and the DOT/DMV/agent-of-your-choice on the spot is the one who gets to make that determination. You can present your case, but ultimately whether or not it gets written up as a violation is subject to that person's interpretation of the rules and your situation.
A friend of mine drives for a company that releases him from duty usually at their ATL terminal. He lives about 4 hours drive time from ATL. The rule says that driving to and from the terminal where you go on and off duty is "personal." But 4 hours? He ran into a DOT officer about 5 minutes shy of the house one day. Guess what? He got a citation for driving beyond 11/14 hours. The officer didn't think that 4 hours was "reasonable." While I can see the officer's point of view, the rule in this case is actually fairly specific in that it places no limit (even "reasonable") on to and from work driving. Friends company backed him up, and at last check the violation has never shown up on DMV record, so maybe it got tossed. I hope so.
The FMCSA answer I got mentioned driving 100 miles to go to dinner as "not reasonable." But what if it is under some circumstance? Let's say you drop a load at a wide spot on the side of the road in the precise middle of nowhere (probably in Nevada, but who knows?). On your way in, the dispatcher called and says, "Hey, good news. There's a load coming out of Widespot the day after tomorrow and it pays super great. Shall I put you on it?" After stubbing your fingers typing "hell, yes" on the q-comm, you look around and realize that your brilliant plan to use the last 3 of your 11 hours to get you to Casinoville for a good meal, a hot shower and more importantly, a 34-hour restart just went up in dust. Oh, well, you think, it's a great job. That's when wife points out that without that 34-hour you won't have enough time on your 70 left to complete the "super-great" you just accepted. And, oh by the way you ate the last HeaterMeal while babysitting a load last weekend and now the cupboard is bare. When the delivery is made you realize that the next pickup is exactly 35 hours away, you can still get that 34 if you just sit still. What do you do?
Answer: it depends. First thing, of course, is go off duty as soon as you hit the parking area on the edge of Widespot. Now, consider your options. You could just sit there for the next 34.5 hours till time to go back to the pickup spot, hoping to scrape enough peanut butter out of that practically empty jar to sustain you, but then you'd have to be sure there was enough liquids available to wash it down. All while listening to the wife express her opinion of you and your "super-great job" and how she was looking forward to that hot shower. Not a good option. Moving on.
Go back to plan A, head for Casinoville and said hot shower and try to muddle through somehow without the 34 restart. You could maybe salvage half of the "super-great" before having to call dispatch and beg off out of hours. You'd look like a fool, of course, and chances of ever getting another "super-great" would go up in smoke, but you'd have something out of it. Better, but still not a good option. Moving on.
Drive to Casinoville anyway, but put it on line 5 (off duty driving). Hmmm. Saves the 34 and thus the load, gets a good meal and a shower, and maybe most importantly, shuts the wife up. Good option! Let's go. But, wait! Is it "reasonable?" It depends. Is there any place closer than Casinoville? Better check before you drive 3 hours off-duty one way. Well, nothing between here and Casinoville shows up on the map or your truck-stop guide. All Rightee, then! We're off. Not so fast, bucko. Grizzled old-timer sitting in the shade of the one bush in the area says there's a little mom-and-pop place about 100 miles in the other direction from Casinoville at Notsowidespot. Good food, well stocked store, and the showers are clean. Now Casinoville isn't reasonable any longer because there was another option. And all of a sudden, a 100 mile drive is reasonable.
Now you could roll the dice, so to speak. Head off to Casinoville logged on line 5 (presuming your company has allowed you enough time on your EOBR to get that far) and hope you don't get challenged by an officer who knows about Notsowidespot. Safest option though is for you to head to Notsowidespot. You can make a case for reasonable if challenged about duty status. If you split the drive between you and wife you might make it even with FDCC's 45 minute limit if you push just a hair (easy enough to do in that area).
Anyway, the point I'm going for here is that "off-duty driving" is a bit tricky but can be a valuable tool for the driver. Just understand what's going on with the rule and be careful.
Stay safe out there, okay?