Pretty much always.
You can be more flexible about your plan and make changes on the fly. Whereas if you're paired up with others, you all have to sorta stick with the itinerary.
Going solo you won't be EFF'd over by somebody being douchey and flaking last minute on you. You won't have to first drive them to their vehicle or home either.
Just get an InReach mini, setup several pre-programmed messages (the ones you can send unlimited of) that can provide your significant other enough of an update about your status so they won't worry about you.
And I HIGHLY recommend getting a setup where your pistol holster hangs under your Bino Harness.
I like to do a screenshot of the overhead satellite view and annotate it using your favorite app like SnagIt to show your hike-in route and denote the general areas you intended to check on or make your sits at. And then email that to your lady, so in case something happens she can give that to SnR.
The one thing about going out Solo... is that once you make a plan and let someone know about it.. ya kinda need to stick to it for your safety's sake. Cause if you stray too far from the plan, and something happens, it'd be much more difficult for them to figure out where you are to come get ya. So you have to exercise restraint to a certain degree while you're out there. So if you spy some place that's a bit of distance away, save that for the next scouting trip.
Another plus of going solo is that once you get back to the truck, it's no big deal to give yourself a sponge-bath with a hand-towel and regular tap water, to get all the sweat off before the long drive back home, so you'll be more comfortable and not itchy on the drive home. Whereas, if you're with others, there can be pressure to hit the road right away. Also, I like to always have a change out of clothes back at the truck with some softer shoes for the long drive back home. It makes a difference.
Another nice thing about solo is that you're not being pushed to match someone else's pace. The older you get and more injuries you have, this starts to become a thing you'll appreciate.
If you're not already bringing a tripod with you, at the very least bring a lightweight skinny one for holding your cellphone for taking the pictures when you're successful, so that way you can set the phone on a timer countdown and run back and get into the shot. So that way it's more than just shots of the animal on the ground, and selfie shots of you beside it's face to prove it was yours.
You'll also need to really discern things like which meds you should always bring with you. For example.. I always bring Imodium, and I always bring Naphcon A eye drops, Acid Blockers and of course, NSAIDS.
And... if you're going out solo... make sure to pester your doctor to give you a prescription for an opiate. If you got one of those Ahole doc's that's leary of anything they deem unnecessary, try asking for just Tylenol #3's. The ones with codeine. They'll likely be more willing to give ya something like that. And with the stupid rules they've passed, they'll only give ya an Rx for like 15ct or 30ct. But that should last a long time.
Cause here's the thing, if you end up having a slip-and-fall and bust something up? It'll suck a WHOLE LOT LESS if you can at least dope-up before having to drag your sorry behind back outta the forest. (Ask my how I know.)
And while we're on the topic of accidents. When you're out solo? DO NOT choose to do anything that seems even remotely sketchy!!! ALWAYS err on the side of boring and cautious, you'll thank yourself later. (P.S. DO NOT trust walking upon any downed log. Sometimes you have to, but proceed carefully, sometimes thing will be fine and then uh-oh, you can feel it's got rot in it compromising it's rigidity)
Oh and definitely bring along a little Sawyer Mini Filter to filter some water. And for that matter, you should always overshoot it in terms of how much water you carry. Especially when an area you're going to is new to you! You DO NOT want to run out of water out there when you've got miles to return and lots of Elevation Gain to return back to your vehicle. That isht is scary as hell!
And of course... as soon as you're back outta the Mountains and get signal... be sure to send a TXT to "Mama" to let her know that you're back out and safe.