To answer this, it absolutely makes sense. It’s extremely useful to better organise math-based notes imo.
As for examples, say I’m writing notes about Lie group representations. Headings could look like
# Role of $\mathrm{exp}:\mathfrak{so}(3)\to\mathbf{SO}(3)$
# Representation theory of $\mathbf{SO}(3)$
# Representation theory of $\mathbf{SU}(2)$
The same goes for note titles by the way.