As you gather experience with SVG and increase your stock of working SVG code, the reuse of that careful effort you invested earlier is sensible.
An important question is how you structure and store the visual components you have created. I return to that question later.
When you cut and paste code from previous SVG projects, you are, or ought to be, using code that has been well tested. You likely invested time in carefully constructing that code and testing its animations, interactivity, and links, for example, to ensure that they were working as you want them to.
Of course, when you reuse that code, you likely do not want to use it exactly in its original form. As you tweak some ...