Microsoft Blend for Visual Studio (formerly Microsoft Expression Blend) is a user interface design tool developed and sold by Microsoft for creating graphical interfaces for web and desktop applications that blend the features of these two types of applications. It is an interactive, WYSIWYG front-end for designing XAML-based interfaces for Windows Presentation Foundation, Silverlight and UWP applications. It was one of the applications in the Microsoft Expression Studio suite before that suite was discontinued.
This is where the power of Blend can be exploited to its capacity. The name says it all, really. As an XA, you blend the code and visual assets to produce the UI and UE. This blending of design and development is the most important concept you should take away from this book.
Microsoft Blend, experienced devs might remember, started out as Microsoft Expression Blend, the company's UI design tool for creating GUIs for web and desktop applications that blend the features of those two types of applications, according to Wikipedia. "It is an interactive, WYSIWYG front-end for designing XAML-based interfaces for Windows Presentation Foundation, Silverlight and UWP applications. It was one of the applications in the Microsoft Expression Studio suite before that suite was discontinued."
Silverlight was introduced as an RIA technology. The core feature is code separation. The View - model are in separation. Blend provides rich support for designing your silverlight apps. which may not be possible with Visual Studio 2010.(btw we are talk of advance designing - something gradients, storyboards, template controls blah blah..). It also contains application prototyping tool called sketch flow. Well Blend also contains code editor. For the designer to dive into code for more grip on designing and behaviors ( designing perspective). Yah but blend don't support advance development tools, like debugging, project source control etc....
If your company is just giving a start to Silverlight project you should be considering the project you have on development - Are they UI specific or simple basic layouts can be fine and yes there professional blend developers out there which can be hired. But still rare, count have increased after SL 4 release.