With RDBMS you have to design the schema first, with NoSQL you don't need to. This is nice when you're dealing with very diverse data (or data you don't even know how it'll look like) or are prototyping. One thing I like about this: You can store your data as it is, you don't have to fit it into your model / world view. You can make sense of it later.

At some point you'll probably have to deal with schema anyway. If this comes at a later stage, you'll have to deal with a lot of diversity and inconsistency on potentially many points. This can become much more painful and time consuming than having dealt with it from the beginning.

If you're thinking about NoSQL as something like a simpler, modern SQL alternative, you're probably having a faster start and a lot of problems in the long run.

Scalability is something, NoSQL databases have for them, definately.