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Read through this post by Rand: https://moz.com/blog/google-says-yes-you-can-still-sculpt-pagerank-no-you-cant-do-it-with-nofollow . Quite old, but still valid in my opinion. So if you want to nofollow the tags only because of sculpting the follow links value, then there is no sense making it. We are using a similar approach with pages we do not want to index, but they are beneficial for our visitors. (similar case to yours)