Lets say I have a site a.com. I have other domains b.com and c.com. If I make b and c point to a.com by IP redirection, people will see a.com website when they type in b.com or c.com on url box. The url will be shown as b.com or c.com although site is a.com. Does this help in any ways at all?
I don't really see a benefit at all. Is there reasoning behind it? IF you are getting backlinks for all 3 just to boost PR for the b.com and c.com domain then perhaps it may be of some value, but doubtful.
It was actually based on a experience I had at my work. We saw one website getting higher rank for some keywords then us just by redirecting to our own site.