Lower a mirror into a flattop guitar... You may notice that the bridge pin holes are chipped out, especially if the guitar has been restrung many times or if the holes were drilled carelessly. The ball ends of the strings can't seat as they should, and that means the guitar may not sound as good as it could. If ignored, this can also split the bridge plate and weaken the soundboard.
The usual remedy is a difficult and potentially damaging bridge plate replacement job. And that's no fun! Ask anyone who's done it.