Is there difference between a tile server or a layer server? Can I load tile in ArcGIS control in WPF from some other source? Can I host my own layer server? Or is there any such thing as layer server?
I am not positive, but I think you mean dynamic or tiled map services? The difference here is the speed with which a web application will work. Tiled services are cached at different levels - meaning a bunch of tiles are created at each level to improve speed. Dynamic services have no cache levels and take longer to load. You would need to use a dynamic service if your data is going to be editted often or is going to have its symbology changed.
ESRI documentation on cahcing map services (tiles): http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/What_is_map_caching/005300000059000000/