Pair programming can improve productivity but it’s most likely hiding more elusive problems. It could be that the feature is not clearly defined or that the team member is not motivated to work because you’re not giving her enough creative leeway. It may even be that she is not technically equipped to implement the feature.
The idea is simple and that’s how it seduces you. As a manager, you may try this technique and see increases in productivity–but are you unlocking the true potential of each individual? It is far more likely that you’re still missing the real issues at hand. Before you adopt pair programming ask yourself what the underlying hindrances are to productivity.
Sometimes it makes sense to pair a junior programmer with a mentor for training purposes but for the most part individual programming with a lead helping to remove roadblocks strikes a good balance. Furthermore, for a small engineering team (2-10), which is the norm for most startups, you should be programming as a team.