What is X11 and what does it do is it worth downloading i've just got a new Macbook air

Question

What is x11and what does it do i've just bought a Macbook Air note book and was wondering if this x11 is worth downloading

Answer 1

In short, think of it as a graphical interface (e.g. window, menus, etc.) that can work across multiple systems. Applications written to use an X11 interface can run on any OS (Mac, Linux, Unix, Windows) with a suitable X11 server (such as XQuartz, mentioned above).
The pros are that such an app can run anywhere. The cons being that it's kind of a lowest-common-denominator effect so it doesn't look like most native applications.
One cool effect, though, is the remote nature of X11 - it's possible to run an application on a remote machine (over the LAN, or even over the internet) and have it display its output on your local X11 system, so your mouse clicks, keystrokes, etc. are transmitted over the wire, processed by the server, and the results displayed on your screen.
As to whether it's worth it - there's no harm in downloading and installing it - it won't do anything unless any app you're running calls for X11, and any application that needs it will tell you so.