Does it matter if I take a photo from within Instagram or import into Instagram? I've begun using Instagram more and more on my iPhone 4S. And typically, I take a photo using the standard Photo app, and then import the photo and process it within the Instagram app.

But I'm wondering if there's any reason that I should be taking photos from within the app. In particular, does photo source affect resolution?
Often, 3rd party apps that can be used as a camera offer different levels of resolution in which they capture the image. Since Instagram is a widely used, and up-to-date app, I would expect they support the highest resolution offered on your device (disclaimer: I don't use Instagram so I can't check with that app).

As long as you have the resolution setting (if available) set as high as possible then you should notice no difference between the built-in camera app and Instagram - you should not lose image quality during import either. 

Otherwise it comes back to personal preference. If you take the images with the built-in camera app, then your photos are automatically in Camera Roll and can be easily saved onto a computer. Camera app is also easy to open from the lock screen.