Partitioning is a solid way to organize your data, which makes finding your files, projects and programs more simple. Separate partitions also make your data easier to backup, saving you from having to sift through multiple folders and directories. You should still use online backup, though, because multiple partitions will not protect you from hard drive failure.
Partitioning also lets you use multiple operating systems on one hard drive. Having multiple partitions is mandatory for that, as each OS requires its own drive. You’ll also want additional partitions for files and data relative to each OS, as intermingling them will create problems. It improves performance, too.