I use it for almost everything. Take ETL type tasks. It's almost impossible to remember where I downloaded certain data files six months after initially creating a project. I put that into the Makefile. Everything I do on the command line, I put into a Makefile. That way, 6 months later when I need to download new data, do some transformation on that data and load it into the database, 'make' re-traces my steps from 6 months ago. Broadly, my ETL makefiles look like this:

all: data.loaded data2.loaded

data.csv: wget 'some url'

%.sql: %.csv sed/awk/custom-python-script $< > $@

%.loaded: %.sql psql < $< && touch $@