I am maintaining 2-3 websites. When I was not aware of multisite install provision in wordpress, I was installing separate wordpress for each of the website. With this feature of multisite I now have only one wordpress Install and created multiple sites within single wordpress installation. It took some time for me to understand but now I am quite at ease. I am able to map Top Level Domains for each of the websites. Only one installation of plugins is enough. Earlier I had to install plugins for each of the installations.