Content recommendations are a great way of increasing exposure of your content. And although they just work out of the box, there is a little inconvenience when using them on a website with subwebs.
When building content aggregations with users’ information Content Search Web Part publishes account names in page source.
When building content aggregations for catalog content in cross-site publishing scenarios Content Search Web Part includes the original URL of the catalog item in the page source.
If you are using Friendly URLs in your website you must use Content Search Web Part to build content aggregations.
When building custom Display Templates for Content Search Web Part always build a corresponding XSL Style Sheet and link it to your Display Template.