How "PageRank leak" would take place in this scenario?
I am new to SEO. I read the following paragraph in a tutorial and I don't understand the second part.  How the "leaking" would take place?  

> Set up a links page to link to other sites so you can reciprocate
> links with them. Link TO your own links page from the site map page
> only in order not to "leak" page rank.

Thanks
How "PageRank leak" would take place in this scenario?
===

I am new to SEO. I read the following paragraph in a tutorial and I don't understand the second part.  How the "leaking" would take place?  

> Set up a links page to link to other sites so you can reciprocate
> links with them. Link TO your own links page from the site map page
> only in order not to "leak" page rank.

Thanks