Fully integrated into the Sitecore editing function, Experience Accelerator (XA) reduces your time to market by allowing content teams to design, assemble, and deploy web content across channels with fewer development resources. IT and implementation partners can be relieved of many page build responsibilities and can focus on the high-impact requirements that usually get relegated to phase two.
Drag-and-drop page assembly
XA’s toolbox has approximately 100 pre-built components that you can use to build any page.
Best practice by default
All code generated by XA follows Sitecore’s Helix best practices around page structure as well as enables the use of experience marketing tools such as personalization and experience optimization.
Separate IA from design
XA’s wireframing tools let the site map and page architecture be completed and handed over to design, so content entry can occur in parallel with design processes.
Source : http://www.sitecore.net