Will the backlinks from 'tag' pages harm my google ranking or will it help in SERP and should I Disavow these backlinks?
Well, it could be dangerous sometimes. Example: If you get a backlink from a blog and in this blog there are for example 20 different tags and you got a backlink from EACH of them... In this case you get many backlinks from a SINGLE domain... Which could be considered UNNATURAL by Google!
That is called "passing juice". By your logic, Google would have banned a site like engadget that make excessive use of tags.
If you first read my post before commenting... Well, it could be dangerous sometimes. I was talking about a website that doesn't have many backlinks and if they have 1,000 backlinks from a single domain, this could be a reason for a ban...