I do this when writing λ, Δ, Φ, etc. in a document on a computer I don't own or when on my phone. It's genuinely faster than scrolling through Word's symbol list, for example.
(Btw for the uninitiated: The x is a chi, pronounced as in Koine/Modern Greek, like in British "hue", first make sure it's a "hj" and then squeeze it even tighter. At least according to Knuth it's a chi, that is.)