The intent of the Builder design pattern is to separate the construction of a complex object from its representation. By doing so, the same construction process can create different representations.
The sample code that usually comes with this pattern is something like this:
I find this sort of code to be extremely verbose and hard to read. Especially when we have a lot of options and things to do. Fluent Interfaces, however, are just an instance of the Builder pattern, and they are basically adding a modern API look & feel to the way we are actually constructing objects. Another thing to remember is that we are dealing with C#, and we have things like object initializers to do a lot of the heavy lifting for building objects. You should use that, for most cases.
NHibernate, for example, has the notion of a Builder, using the NHibernate.Cfg.Configuration object. It allows us to put all of the construction / validation code in one spot, and then the actual runtime code in a different place (and can assume a lot about its invariants). It also allows to do a lot of interesting things, like serializing the builder object (to save building time), which is something that you usually can’t / hard to do with real objects.
That said, you should be careful of code like the one listed above .What you have there is an overly abstract system. Requiring multiple steps to just get somewhere. If you find yourself feeding builders into builders, please stop and think about what you are doing. If you got there, you have not simplified the construction process.
Recommendation: This is still a very useful pattern. It should absolutely not be used if all you need to do is just setting some values. Reserve the Builder patterns where you actually have logic and behavior associated with the building process.