Domaining is becoming more popular these days. There’s a mindset that thinks buying a second domain and linking to your main domain will help your rankings in the Search Engine’s. And, it certainly is possible if done correctly. However, if this is just being done as a pure SEO play, I wouldn’t recommended it.
You should have a serious purpose for the second domain for this strategy to even have any effect. And, it’d be best to use an aged domain, with different registration information.
Some uses for the second domain might be to use it to create a microsite, and/or another ecommerce site, then slap some links on there to your main domain. If you’re reusing an old website, perhaps you could redirect or reuse the existing URL’s.
Try not to have to change the domain owner registration. And, register it for a long time…like 10 years plus. Host it on a different IP address than your main domain. And, fill it with great content. Perhaps use it as a company blog of some sort. It might be fun to use it as an experiment in Predictive SEO.
But, if you’re just using it to just boost your main domain in the rankings, then once again…I wouldn’t recommend it. You’d be better off using your resources and budget to develop and executing a custom SEO Strategy. If you don’t have in-house resources, or expertise, you might want to consider using an SEO Consultant.