What if I move one of my popular websites under another popular website?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Search Engine Optimization Tips & Techniques: Hey friends need to get answer for one query. How much benefit i will get if i move one of my popular website , under another popular website. I mean if create a deep folder level for one of my website and include my another website as a sub folder then is it going to be beneficial for me?
  
  My new folder will be some 4th or 5th level down in my website structure.
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  Andy Wigglesworth: +Search Engine Optimization Tips & Techniques ;
  
  I think the question would be, do these sites need to be together?
  
  For example, there's not much point having a hair salon website under a welding company.
  
  Also, are your users going to benefit from you doing this?
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  Search Engine Optimization Tips & Techniques: +Andy Wigglesworth well basic idea was to bring one blog or forum website under main website, blog is all related to industry where ; website operates. But because of current URL structure that new domain will have to come some 4th level down in current structure, so is it of any use to do this activity.
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  Andy Wigglesworth: If they are for the same company, personally, I would probably merge them.
  
  Obviously make sure you 301 redirect urls over to the domain that you are moving it to.
  
  I guess the other option you could do rather have 4th level down, have sub-domain blog.something dot com?
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  Abhishek Kumar: +Search Engine Optimization Tips & Techniques ;
  If your websites’ content is similar enough"
  
  Because both site might have back-links and it will be from their relevant domain. So if the site which you want to merge into another popular site should be of same business/industry.
  
  Or else i think links pointing to that site might harm your site because of the latest Google updates.
  
  Please correct me if i am wrong.
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  Search Engine Optimization Tips & Techniques: +Andy Wigglesworth Thanks Andy, but having a subdomain is not an option here. 301 redirection is one option but by the consolidation which part of my website will get more benefit, root folder or sub folder.
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  Search Engine Optimization Tips & Techniques: +Abhishek Kumar website content is relevant but back links are not any issue. Only issue is is there going to be any benefit to root domain due to this consolidation and also how beneficial it will be as URL of root domain will become excessive longer which won't be completely visible in Google search results.
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  Abu Aslad: Very Bad Idea ... Not useful !!
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  Search Engine Optimization Tips & Techniques: +Abu Aslad ; can you please provide detailed explanation.....
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  Geoff Smith: 4th level is really deep down. It sounds risky. Personally, I wouldn't do it.
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  Andy Wigglesworth: Ok, perhaps it's just me being a simpleton -
  and I probably should have asked this sooner - ;but why does it have to be 4th level...
  
  So why cant you have...
  
  www - somedomain - com/blog/human_readable_url
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  José Manuel Gilpérez: It sound to me that being in 4th level is going to be less accessible, so I do not find a good idea a site that is going well to take it to a place more difficult to find. I wouldn't do it cause I think it won't work in the long term.
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  Ryan Dinelle: As a rule of thumb, never sacrifice end user experience for the sake of SEO.
  
  That being said... 4 levels down is a bad idea. Anything of real value should be no more than 2 levels in. Anything more, and you end up with extremely long URLs that search engines could see as spammy.
  
  If you merge the blog into a 2nd level folder, and then set up the appropriate 301s, it will preserve close to 90% of your old domains's authority.
  
  Hope that helps some.