Besides, your friends may be 100% behind you in your new venture, but, in case you are hoping to involve others who have actual money to invest, you may need to be able to make a convincing case. Wouldn't it be nice to have anticipated possible questions and be ready with plausible answers? If you are risking your own money, that is perhaps even a stronger reason to do some indispensable planning.
I often see people split into two camps. On one hand those who almost ignore competitors in their business plan, because they do not want to think about the issue yet and feel so confident they have a great idea for the market regardless. But I recommend not being overconfident when it comes to competitors. They are still there for a reason, they are still around and in business for a reason, so view them with that in mind.