This image is the "daily driver" for many network students. Because it uses roughly per instance, you can build a full "Core-Distribution-Access" campus topology on a single machine.
For students pursuing CCNA or CCNP certifications, this specific image is a "goldilocks" choice because it supports: i86bilinuxl2ipbasek9151gbin repack
Note: Many IOS images are cryptographically signed; modifying them without access to signing keys will usually lead to failed signature checks and cause devices to refuse to boot or operate correctly. This image is the "daily driver" for many network students