Not every computer has a GUI. Sometimes it's better to build the project in the background where it can be done automatically instead of requiring a person to manually stitch the build components together.
Also, GUI projects are quite fragile. You can't take an Eclipse GUI project and build it under IntelliJ or vice versa. Worse yet, some vendors have been known to change their GUI project definitions so radically between releases that a project built on an old IDE version won't build on a newer IDE version. That can also happen with batch build systems such as Maven, but it's less likely, if for no other reason that you don't have two points of view to consider (human interaction vs. persistent copy of the project spec).
"privilege" comes from the Latin words for "private" and "law" (legal) and dates to feudal times. To "claim privilege" meant that you were above the laws that applied to the common people.
Thennam, Even if everyone on the team is using the same IDE, it helps to build the jar, war or ear from a build tool. This prevents "it worked on my machine" syndrome. This is where someone accidentally (or on purpose) doesn't commit something and the deployable artifact can only be built on their machine.
Also, it embeds the instructions for how to build the artifacts in an executable (build script) rather than in a document or in people's heads.
In addition to the comments already made, in more complex projects an IDE actually *can't* do a full build.
The Ant build for our project currently does
- generate source code from meta information (such as XML schemata) - compile - run unit tests - build jar files - assemble thirdparty jar files - assemble license information for thirdparty jar files - build javadoc - build war files - run acceptance tests - generate a number of PDF documents from meta information - generate a number of XML files - assemble example source code - assemble example configuration files - and probably a number of other things I currently don't remember
I don't know of any IDE that were capable of those tasks, let alone with the flexibility we need.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus