If I will never want to dual boot two OS, then should I have number of partitions in 500GB main hard disk in notebook for any good reasons?
Or What are the other reasons someone can have multiple partitions? Also what is the best strategy for partitioning?
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.
Some reasons other than Dual Boot:
For example, I can back-up a Disk E with all my user data. This answer given in more detail in some other answers to the question
In the old days, your mail server or your log files might fill up your all your disk space, causing many headaches for the sys-admin, including the ever humorous "108% full" disk drive.
This was a common Linux, and perhaps other, security thing. You put your kernel and some other files on a "read only" partition to prevent malicious users from changing those files. When it was time for an upgrade, the sys-admin had some hoops to jump through to get the partitions writeable.
To tell the truth, for single user machines, I find partitioning to be too much of a headache. I don't even dual-boot anymore, I use some kind of Virtual Machine.
For servers, the partitioning scheme depends on what kind of services the machine will be offering.
Short version: makes it easier to format the OS/home partition when reinstalling or changing you OS.
As other suggested, I used to partition my hard drive in 2, one for the system and one for the data.
But today, I will be the other voice because I tend to keep only one partition. Here are my reasons:
As EricJLN said, it is smart to put all your files and user data on a separate partition. This way when you want to reinstall next time, you won't have to move your files around, just erase the system partition and reinstall on that one.
If you are running a system that supports mount points in folders (like linux, not sure if osx does, but probably), you can simply let your home-folder or whatever your system has be the separate partition.
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.
