1. Do what you want!
Want to go see a hockey game? Meander around the city for six hours without actually stopping to refuel? Hang out in a coffee shop all day? Ain't nobody who's around to tell you otherwise! To do what you would like to do is an incredible gift since you don't need to take anyone else's opinion into account. I'm big on museums and libraries, so my time in London was perfect as I was able to wander around the British Library without any grief from friends who wanted to go shopping or hop on the London Eye.
2. Go at your own pace
Unlike if you were with a few friends, there's no pressure to walk faster if they're power walkers -- and likewise, there isn't the stress of trying to herd your heavy-footed buddies to keep up with you, either. I saw nearly all of the major sights in Venice in six hours at breakneck speed, only to calmly pad about the city on the following few days. If I were with friends, there'd be no telling if I'd even see the Doge's Palace.
3. Flexible scheduling
Your plans can change day-to-day thanks to a multitude of reasons. If you travel by yourself, it's a lot easier to reschedule something or change things around if you don't need to check with your traveling partner to see if they're okay with it. Come back to your lodgings in between sights to take a nap! Nobody will, nor can, say anything!
4. No social requirements
At the end of the day after the hustle-bustle of a tourist's life, it's nice to unwind by taking some time for yourself to mellow out. Of course, if you had a packed day with a travel partner, tempers may fray to the point where dinners may become awkward. Party of one? Crisis averted. You can truly zone out when by yourself without the mandatory checking in of your friends, and making sure everybody is on page for the night's activities.
5. Know thyself
It can be incredibly daunting to travel by yourself. Things go wrong! Public transit may delay, and you can be in a city at 10pm at night without a clue how to get to your destination, as what happened to me when I landed in Milan late at night. But after these hurdles, you realize how strong you can be in the face of setback and uncertainty. Some people are born with an innate sense of steely independence, and for others, it's learned through trial by fire. I'd always identified myself as someone who tends to err on the shyer side of a personality, and it was only through lots of independent travel that I learned how important my voice was, and how equally important it was to believe in my voice. Traveling alone can also bolster your gregariousness, as I found when I was in Dallas recently. Nobody will go out of their way to take care of you, so you need to make sure to speak up to make sure you are taken care of!
You can split everything with friends. Hotel rooms are half the price with a girlfriend to share with you. Dessert isn't fattening if someone's taking on half the calories. But if you're by yourself, you can't really try out that buzzy restaurant nor is an Uber your go-to when on a budget.
2. Selfie Saturday? More like Selfie Everyday
Your friends should be chill enough to volunteer to take your photo on an outing. When you're solo, though, it's tough to find someone to be your photographer, especially if you're doing something in nature. Here's a tip for cities: when my friend and I were in London looking for someone to take our photo, we looked for fellow Millenials who were traveling in at least a pair, and were dressed nicely enough to not steal our phones. We tried elderly couples in the beginning, but they just, like, so didn't get our best angles. Stereotype much? Perhaps, but is a middle-class trio of British girls going to run off with our iphones handed over in the middle of harried Piccadilly Circus? Smart money's on the option 'no'.
Your new-found independence and freedom from dealing with attitude or differing opinion is intoxicating, until you're faced with endless stretches of being by yourself. An easy way around this is to just start politely chatting up anybody around you who is part of the service industry. Not only do they have a friendly face to break up their monotonous day, but you can get invaluable tips and feedback from a native of the area. I've gotten insightful recommendations from museum security guards before that were truly helpful.
4. Loss of creative input
Sometimes, the best sights or activities when in a foreign land only comes about during a random stroke of inspiration during a conversation. In fact, the best trip I've ever gone on with friends was one to the Scottish Highlands. I would have never thought to have done that if I were alone, although when I found myself on an extended stay in Edinburgh later, because of this previous experience, I ended up joining a one-day tour by myself to Loch Ness and Glencoe.
5. Safety risk when socializing
You have to be extra cautious of your surroundings, especially when in a sketchy area or at night. If drinking, your safest option would obviously be in the hotel bar. This happened to me when I was in Berlin alone, as I made conversation with the bartender and let him know that I was here alone. Sitting at the bar, a man sidled up and tried to engage me in a conversation I was not a willing participant in, and the newly-befriended bartender came up to me and announced that my 'table was ready, apologies for the wait' when I actually hadn't had dinner plans. He ended up escorting me to the nearby lounge and gave me dessert on the house, making sure I was safe from that creep -- but I was lucky in having someone like him look out for me.