You can keep a lot of music and videos on your Mac because it likely has a larger storage capacity than your iPhone or iPad. Fortunately, you can still easily share your entire iTunes library with all your Apple devices without physically transferring a single media file.
Normally it can be fairly difficult to reliably share media between several devices in your house but with iTunes Home Sharing, it’s easy. Best of all, technically you’re not strictly limited to Apple hardware. As long as you’re using iTunes, you can even share your library with and from Windows-based computers. That said, if you’re using a Windows PC, storage capacity is also likely not a pressing issue.