The Pros
1. Complete Independence
The feeling of absolute independence is for me unbeatable, and the main reason I tend towards solo travel. Just knowing that nobody you know, has any idea exactly where you are and what you are up to at that moment is completely liberating.
2. Meet more people
I found that it is always easier to meet people when travelling alone. Possibly purely out of necessity, solo-travel will result in meeting more friends and even coming out of your shell a bit (if you are a shyer type). Travelling with your friends from home gives you the excuse to remain introverted which can seriously hamper your travel experience.
3. Flexibility
I love having the ability to live by my schedule. Travelling solo means you can wake up one morning and think "I don't really feel like taking the 15 hour bus today," and then you just don't or maybe you decide to take a 10 hour train in the completely opposite direction of what you had originally planned based on a suggestion of one of your new found friends.
4. No conflicts
Travelling with a friend, you are likely to have bad days when you are not getting along and don't even want to see the other person. It's not that you dislike your travel mate, or that anything is wrong with them, it's just that spending that much time together can begin to take its toll. When you are travelling alone you are unlikely to ever face these conflicts, and if you ever tire of a person at your hostel, you can pick up your pack and move on.
The Cons
1. Some lonely days
I personally enjoy being alone a lot (makes me sound really cool, I know) but even I find the long haul buses and trains can be trying. I also found it can be hard to meet people when you are not in a good hostel or if the town you are in doesn't have a backpacker hostel or hangout.
2. More expensive
When there is an abundance of Hostel's with dorm rooms(as in Europe) this isn't much of an issue. In Asia, however, many towns have only guest houses and the cost of splitting a double room is much cheaper that a single room (which is often just a double room with only you in it).
3. Lots of self taken pictures...
I could put together an entire album of photos of me taken with an outstretched right arm. None of these photos are particularly good or frame-able and I can't help but think that I would have many better pictures of myself if I had been travelling with a friend. As a result I did learn how to master the self-timer-shot though (pro?)
Personally I will always prefer to travel alone but I understand that it is not for everyone. If you are going travelling for the first time start with a friend but have the mutual understanding that at some point in the trup you may go your separate ways.
