chroot has nothing to do with dual booting. The idea behind chroot is the ability to switch one program, or one shell, etc., to a new root directory, allowing you to have multiple "systems" at the same time. "systems" is in quotes because there is still only one Linux kernel running. This other "system" is an additional set of the code tools, home directories, etc. So, if you are on an x86 machine, and are trying to build some software for ARM on your machine, you could create a chrooted environment whose /proc tells the software that it's on ARM, an ARM GCC toolchain, etc. (There are many programs that do that). The other thing chroot can do is some very limited sandboxing, that combined with something like SELinux and basic Linux permissions, could create a relatively secure sandbox, in which this application thinks it's on a different system. Another use of chroot would be testing. If you have an application that does different things based on some system directory, you can create a chroot to test it in.