Producing tight systems is necessary, no matter if you produce tanks for the space shuttle, automotive gas tanks or gas ditribution systems. Other typical leak test objects are air bags and pace makers, and anyone can understand what a disaster these could cause if not tight.
Leak testing is often done with a gas or gas mixture together with a "sniffer" which is a specialized mass spectrometer (MS.) Gas tanks and distribution systems are checked with helium or helium mixtures while automotive systems often are checked with sulphur hexafluoride.