Thank you for answering.
My first reaction was that you obviously have no idea what you are talking about. For example, you can't change the allocation of space on a hard drive without disrupting the file system. Therefore, if you repartition your drive you have to format the new partitions with a new file system before you can access them with an OS. This should be quite obvious. In fact it's so obvious that I considered that you might be trolling. Either you're trolling, or you like posting arguments about things you really don't understand.
Fortunately I wasn't aware of this fact before. I have repartitioned my hard drive without having to format it (the old or new partition; of course if you like to twiddle with semantics then the new drive is formatted in a sense, but the data is not lost). Like I said, it can be done with proper tools, like partition magic for one. These proper tools can change the partition tables without losing any data (what comes to Windows).
Then I saw you are from Finland, and considered that English is probably not your primary language. Maybe you misunderstand the "formatting" we're talking about. Since you are probably an intelligent person, I gave you the benefit of the doubt.
I would always wish to know what I might have misunderstood, other than simply being put down for having english as the foreign language. You can't learn an error without knowing where you've gone wrong, lest defend your argument.
Generally "formatting" means the act of setting up a file system and erasing the information of all of the pre-existing data in the clusters assigned to the new file system, resulting in an empty file system. Though, the data written to the disk can be still retrieved, unless the clusters are overwritten with new data.
So, which is it? Do you not understand what we're talking about, or do you just argue things you don't understand?
Well, I do have 17 years of experience with PC systems, preceeded by experience of Amiga, Atari and Commodore 64; and even more experience in english (especially back then there wasn't much of a choice). Though, that is not to say I couldn't be erred or indeed misunderstand. However I can understand english much better than I can speak it, so do not let my grammar errors make you think otherwise.
If you really can't think of a reason why someone would want to format a drive on occasion, then you really don't have any credibility with me in this thread.
In the case of re-installing Windows I can't. Otherwise there's only a handful of situations where you really need to reformat. Of course everyone is free to reformat their HDD as much as they wish, but most of the times I find it to be too much of a hassle. Yes, I'm lazy and I will always try to find a way around reformat; re-installing Windows is the easiest.