I've mentioned pair programming before in the context of the psychology of extreme programming, but I haven't said too much about it. This is because I've had very little first hand experience with it. Well, in the last couple of months I've spent a lot of my time pair programming, and here are my preliminary thoughts.
I have argued that pair programming can cut down on distractions. I find this to be true. When working on my own if I execute a command that I know will take 5 or more seconds, it is very tempting to take this break to check my email or read a slashdot article. Unfortunately, while I justify this as being efficient, in reality it turns a 5-10 second pause into a couple minute pause. The change of context also flushes some registers, err.. short term memory, making it harder to be as focused when I first switch back to my development tasks.
When someone is looking over my shoulder, I am not going to make that context switch.
I find that my enthusiasm for projects ebbs and flows. I'll be gung-ho for a while, and then my motivation will slip away. Its easier to keep working in a pair, both from the peer-pressure that you don't want to be slacking, and just the fact that its more fun.
I've always read that pair programming is more productive than one person working alone, but not twice as productive. (measured in terms of how much code gets written per unit time). My experience of the past couple months agrees with this. Of course this ignores other benefits from pair programming, like potentially higher quality code, and the implicit cross-training that happens.
Pair programming definitely cuts down on mistakes. While the person on the keyboard is directly thinking about what they are doing, the backseat driver can focus on this big picture. These two different views helped us realize shortcomings that would not have been found until production had either of us been working alone. Also, when bugs were encountered, having two people (who think differently) looking at them, meant we were able to resolve them quicker.
There are a few problems that I encountered with pair programming. The most obvious one is scheduling. The two of us paired up have different schedules in our personal lives, so we don't show up at the same time, or leave at the same time, or even take our lunch breaks at the same time. Plus we both have other professional responsibilities that sometimes require one or the other's attention at various times at the day. Thus an eight hour work day results in only four or five hours of useful pairing time.
The problem that I didn't expect was energy drain. After a couple of weeks of doing primarily pair programming I felt mentally exhausted. While we got a lot done, it wasn't a pace that I can maintain indefinitely. I think the little breaks that I normally build into my day, which were missing when pair programming, helped keep me fresh. I suspect that I can address this problem by intentionally scheduling breaks when pairing up.
it is most effective to work alone for a whileThe third, and most important, problem is problem solving. There are obviously times when two heads are better than one. But there are also times where the two heads need to work on their own. To solve difficult design problems, or to come up with innovative solutions to a problem, I truly believe it is most effective to work alone for a while. Then, after I've had a chance to think about it in my own way and come to my own conclusions, is the time to meet and discuss the ideas with others. i.e. if we work together on a solution, we will come up with one solution. If we work independently, we will come up with two solutions, from which we can then draw a third solution that is better than what either of us came up with independently, or if we had worked together all along.
Pair Programming has a place in your toolkit of software development skills. I think it can be really helpful when working on software that you want to be reliable, you want more than one person intimately familiar with the code base, and which doesn't require too much innovative problem solving. However, like most things, moderation is the key. There are definitely times when pair programming will hinder you.
If you have the opportunity, give it a try. However, be open to the fact that it isn't best for all situations, so don't force it if it doesn't fit.