Buying new domains to help with SEO

[Socialdude]

Hi,

Does buying new keyword related domains and 301 redirect them to my site have any seo benefit?

[ManiKarthik]

You could. But make sure that the pages in there have some sort of "in-context" relevance to your pages as well. This would be better than a blind redirect. For example: abc.com/apples should be redirected to yoursite.com/fruits. No thumb rule here, just trying to make it effective for the old site.

[activitysuper]

What about domains that once had a life?

For example lets say a competitor with 5,000 external links decided to end and you got their domain, could you redirect it to your site and pick up the benefit of those 5,000 links?

[SimonCullum]

Exactly, Robert is spot-on there.  Buying new domains (with no prior history) will have literally zero SEO benefit.

The only reasons to do so are for future plans to host a site on them and/or brand/trademark protection through owning such domains.

[Socialdude]

cheers thanks I just needed some clarity on this topic

[RobertFisher]

None whatsoever. 
I am assuming you are buying a domain name XYZ.com and not an active ongoing site with pages that would be 301'd to your urls. A 301 says content that was originally here has moved to there...permanently. So, if there was no content and no links, there would be no benefit.