The right travel buddy pushes you out of your comfort zone more than you’d push yourself
The most common argument for traveling solo is that it pushes you -- that its value comes in not having anyone else there to distract you from your own instincts and the important work of Finding Yourself. But if the point is to push yourself outside your comfort zone, the easiest way in the world to get a false positive is to spend your trip factoring in no one’s taste but your own. Stuff isn’t automatically located outside your comfort zone just because it’s new. Being alone in an unfamiliar place is discomfort enough -- you’ll likely seek comfort in the types of places or activities you already know you enjoy, which isn’t exactly growth.
If you’re traveling with someone, you’re factoring in a whole external set of beliefs, needs, perspectives, and interests that might actually be outside your comfort zone. Your travel companion may very well have a totally different itinerary planned, activities you may not think you want to do or, quite simply, would never have occurred to you. If he was alone, my backpacking buddy never would have gotten scuba certified and joined me on a dive in New Zealand and Indonesia, or done any of the adrenaline-filled stuff, or tried mango juice. Likewise, aside from never remembering to add the frequent flyer number to ticket purchases, I’d have stupidly skipped over most of the domestic leg of our trips, like all the national parks and flyover country, plus Canada. I’d never have never gone fishing in Zambia. I’d have missed so much.
Everything’s so much cheaper when you split it
A lot of the online rhapsodizing about solo travel makes the condescending assumption that the solo traveler in question has literally never spent any time alone before. But, more problematically, it implies that the only people who get to truly understand themselves, and the world at large, are people with a lot of money -- something you need in order to travel no matter what, and in vastly greater amounts in order to travel alone.
Backpacking, and traveling recreationally in general, is a colossal privilege. But you know what? It’s also pretty uncomfortable, physically. As with most things, the amount of money you can save on hostels and hotels is inversely proportional to the level of comfort you achieve. If you’re at a hostel where a bunk bed costs, say $30-$40/night, a private room probably costs like $50-$60/night. If you’re anything like me and are inclined toward cost-cutting measures like sleeping in your car, the bunk is already a splurge. But when you’re traveling with one other person? All things split equally, you’re spending less money to be more comfortable, and this can still apply even if you’re at a nice hotel or some whimsical Airbnb.