You should do nightly builds to ensure that your codebase stays healthy.
A side effect of doing nightly builds is that it forces the team to create and maintain a fully automated build script. This helps to ensure that your build process is documented and repeatable.
Automated builds are good at finding the following problems:
- Somebody checked in something that breaks stuff.
- Somebody forgot to check in a necessary file or change.
- Your build scripts no longer work.
- Your build machine is broken.
Doing this nightly ensures that you catch such problems within 24 hours of when they occur. That is preferable to finding all the problems 24 hours before you are supposed to deliver the software.
You should also, of course, have automated unit tests that are run for each nightly build.