Let $I\vartriangleleft A$ be an ideal of a commutative ring. Consider the submonoid $1+I\subset A$. What is the geometric interpretation of localization at this submonoid? How does it relate to the quotient $A/I$?

I asked this on MSE and received some interesting comments, but I would still like to know the big picture and perhaps some examples. Taking e.g $\langle x\rangle\vartriangleleft A[x]$, the localization $A[x]_{1+\langle x\rangle}$ seems like it takes $x$ to something "very infinitesimal". I don't recognize this ring as the functions on some familiar "space" as e.g the dual numbers are the functions on an infinitesimal line segment. What is the idea here?