As mathematicians, we are sometimes tempted to provide a symbol for every quantity or object in our paper, but this deteriorates the work’s readability as it overloads the reader.
P.R. Halmos once wrote, “the best notation is no notation.” If you can avoid introducing a new symbol, then the text is often more clear and the reader has one less thing to remember.

One rule of thumb in this vein is to never use a symbol only once. Consider the following definition:

A function $f$ is called a homeomorphism if it is continuous and has a continuous inverse.

The symbol $f$ serves no purpose since it is not used elsewhere in the definition. Thus, it can be omitted.