I've learned about spherical harmonics (Legendre polynomials $\longrightarrow$ Associated Legendre polynomials $\longrightarrow$ orthogonality relations $\longrightarrow$ normalization coefficient(s) $\longrightarrow$ laplace's equation in spherical coordinates [not exactly in this order, and with other tidbits here and there]). However, I've only done a few spherical harmonics expansions, such as simple symmetric functions, functions explicitly given by a finite number of spherical harmonics (in cartesian or cylindrical coordinates usually), etc.
Given this, I'd say my knowledge/understanding of spherical harmonics is minimal. I wanted to know, how important is a thorough understanding of spherical harmonics for working physicists/cosmologists/scientists? Are they of much use outside of working problems in an electromagnetism and/or quantum mechanics class? Would it be worthwhile to study and work them in a lot more detail?
(I didn't know if this question should be tagged as a soft-question, so please forgive me if it should)