There is no requirement to use the tool provided by the SD Association. Formatting the card in Windows using the Windows formatter may also work.
However, there is a strong recommendation to use the tool. At least for SD, SDHC and/or SDXC cards. Different OSes and different formatting tools may have varying ideas about how to format an SD-card, many of which will not result in a smile on your face when trying to boot an R-Pi with it. At least when using this tool you'll be certain the result will be "up-to-spec".
For example, some formatting tools, may only format the first partition or use less compatible formats like FAT, NTFS or exFAT. This results in a card of which the full capacity is no longer available. SDformatter will erase the entire card and create a single partition formatted to FAT32. FAT32 being the format of choice for use with the Raspberry Pi.