josegonzalez/homebrew — comment on commit 12ab79a73ceadab60c2b0fb1624c0a1ad11b6914
File: Library/Formula/imap-uw.rb line 18
By josegonzalez:

Because those binaries would otherwise be unavailable to the system and then are cleared at the end of the brew installation. I recall needing `c-client` to properly install the PHP `imap` extension. The others are also useful for other applications, so it made sense to move them into the prefix.