There is more to website design than knowing what content goes on which page. You need to plan ahead and decide how the pages will work together and which pages will be linked to one another. If you don’t then you will wind up having design problems at some point in time. You need to know where a certain page belongs in the page hierarchy. You need to design a site or user flow in order to have a properly functional site and in order to do this you need to know what they are and what the difference between user flow and site flow is.
The site flow and the user flow are not the same thing though people may think and tell you so. A site flow can be described simply as a blueprint of a building, it gives you a view of the site so you know the complexity of the site and how the pages are linked together. It shows you the basic structure of your site.
A user flow on the other hand tells you the distance between two points and will tell you how you can get to the desired page and in how many ways. In simple words it is like a map. The important thing is to know which to use when.
The site flow gives you a clear cut hierarchy of the site so you know the complete extent of your site. The length and breadth of the site. Other members of your site can also get help from the user flow especially developers who need to keep track of individual pages.
User flows are used to analyze complex tasks like linking pages in a process. The user flow helps developers know how the site is interacting with the user’s behavior.
At the end I would like to say that although flows are important you should not spend all your time working on them. At the end of the day you have to have a site up and running. Think about it too much and you could be headed south.