Do I need Partition for any good reason if I only have single boot?

"You might want a separation of concerns in how your data is being handled. So one partition for your Windows/Program files and another for personal data (videos, music, documents). The advantage would be the ability to change your Windows install, upgrade, reformat and so on without needing to touch the personal data. If something, software related, goes wrong with your Windows install then it won't affect the personal data either.

Of course it doesn't protect against hardware failure. So don't treat the above as a decent backup strategy."

Short version: makes it easier to format the OS/home partition when reinstalling or changing you OS.

"Having 2 partitions, one for Windows and application, is handy if you also have a disk imaging program like TrueImage or Ghost. The Windows/apps partition can then be quickly/easily imaged/restored as required without touching your (often large) data partition.

On the other hand, casual users can often think saving data to the second partition is somehow safer or like a backup. This is of course a very risky way of thinking.

Many laptop manufacturers create 2 partitions by default on new computers. However the D drive partition is either not understood or is completely forgotten about. For a causual user a single partion with a separate external backup drive is better then 2 partitions on the one disk."