When you install a custom component inside the IDE, the package is normally only used during design time.
When you drop a component onto a form and compile your application, you have to provide the dcu and dfm files for the compiler and linker. This is the same for all other used units, too. Just have a look into the lib folder of Delphi.
If you compile with packages you can omit the dcu and dfm files as they are contained in the package dcp file. In that case you have to provide all needed bpl files together with your exe file. I am not sure if this is what you want.