You can learn from the experience of people and companies who are working with Yaffs. Thousands of developers have used Yaffs successfully, and commercially-licensed Yaffs has many customers that use it repeatedly. Have a look at the mailing list - it's a great place to start if you have some questions.
http://stoneboat.aleph1.co.uk/cgi-bin/mailman/listinfo/yaffs
The searchable archive of postings is at http://lists.aleph1.co.uk/lurker/list/yaffs.html Or search online to see the variety of work done with Yaffs as its basis - from research papers through to skunkworks projects for testing particular concepts.