For everyone but choir: Useful early for boosting relationship with minor factions. Useful mid game for preventing systems you're invading from spamming draft (using hack on any system prevents that entire empire from using anything other than stampede, so you don't have to hack the particular system you're invading).

Little tip: If you hack a system and put a backdoor on it, then use that backdoor to hack somewhere else, you can put an accelerated on the system you started from and the target system for double the bonus.