Lots of companies have more than one website. Not many have total control over them all from a single administration area. The options and competitive advantages it brings are many:
add a product once and move it to as many websites as you choose
keep your corporate theme or deliberately make your shops look different
have a different web address for each online store
have the freedom to vary your prices across shops - same or different
manage everything centrally or delegate responsibility for each individual store
dispatch and organise orders from one place
take full advantage of the circle of links that are under your control
copy each shop then market to different target groups
concentrate key words in each shop
perfect for franchises and adding local identity to individual units