As Instagram prepares to map your Instagram username on their service to your Facebook account name, tagging people in photos is a logical step. Identifying individual in photos is very powerful helping map and strengthen the social graph Facebook continues to build.
Imagine you post a photo in Facebook now, all the prompts ask you to please tag the other person. Including the recognition they use to actually put a square of peoples faces. It encourages you to do that tagging step of the other person. It encourages you to expose more of your personal life connections via photos that share life moments.
Having a photo of yourself that also includes others allows Instagram (Facebook) to further use their algorithms to build trusted contacts and close friends. How often are you getting prompted to add someone now on Facebook and you wonder how they figured out you know them? Mutual connections are a strong indicator but being in a picture almost guarantees you know them.
A lot of people seemed to doubt me when I first posted how Instagram and Facebook were moving closer together. Here we are at a common feature with common security measures (you can remove yourself from a tag or set it to manual for approval only) between the two networks as Mashable noted.
You may have built a separate identity on Instagram with alternate connections. Soon this will come together and your Instagram pics will be placed in your Facebook profile and those tagged will be suggested as friends.
I am just calling it now. What are your thoughts?