One of the biggest downside is that the startup time for python is significantly slower than the shell. With just one script this isn't really noticeable, but if you're composing a lot of small scripts together, python becomes noticeably less responsive for interactive commands than bash.

Along similar lines bash's syntax is incredibly streamlined for composing standalone scripts and programs through pipes. A simple bash one-liner like the below would be much more awkward to write in python:

> diff <(netcat $server | grep town | sed 's/street/St' | cut -f 3 | head -n 5) <(cat ./$(psql $query).dat)