A good obi is essential in every form of Japanese swordsmanship. In comparison to other martials arts, Japanese swordsmanship tends to use a wider obi. This to offer extra support for the sword.
Without a good obi (too rigid, flexible or small) you'll notice that the your blade will 'pop up' and not stay horizontal. A steady blade is very important for a good nukitsuke/nukiuchi (drawing of the blade).
This traditional kaku obi has a length of 395 cm long and 9.5 cm wide. They are directly imported from Japan and are made of very high quality cotton.