Is there any benefit to adding outgoing links on your site ? Though they may be useful but it redirects the traffic. Is it good seo ?

Think of your visitors. Of course you want to recommend other sites that will be useful to them. You'll then be an interesting place to find good information and links to good infrmation. There's evidence that sites that link out to nothing sometimes don't rank as well as those that do.

It's only natural that you would link out to other sites that are on your site's topic. I would think the search engines would expect that.

If you don't want to link out to your competitors, then link out to a wikipedia page on your site's subject.

I work on the basis that my visitors have to leave one day (I don't distribute pensions!), so it's best to offer some 'recommended' follow-ups. If your site is good, people won't jump at the option, on the other hand, if your site is helpful, return visits are much more likely.

I also believe that a positive linking policy does help with Google - I believe it's the Last SEO Secret.

Sadly, I have no way to prove it

If you are asking strictly from an SEO Ranking perspective, A link to another website from your website does nothing.