Biox, in the situation you mention, the only use I could see for linux was using a livecd to recover data, in which case you dont even need linux installed at all. There are also many windows based bootcds that one can use to recover, linux is far from the best choice if you ask me in this matter (especially if you use dynamic disks (such as is the default in windows vista), ntfs partitions (which linux still has problems with), or a software raid array)). Tools like
Ultimate BootCD and
Hirens Boot CD both include tools that are designed for a windows system and include data access to these types of partitions or disks.
As for advantages, having a data partition means you can reinstall your OS at any time and not lose your data. I have my primary HD partitioned in 5 sections, one for different types of data. This has helped me as now, I can transfer data off my os partition (whatever there is), and reinstall without affecting the other partition. My data will remain in tact, and if windows chooses to remap the drive letter after a reinstall on that drive, I can simply change it back and go about working the way I had previously.