Many NextGEN Gallery users take advantage of protecting their galleries with passwords. This is done using the WordPress feature for password protection of posts and pages.
A use case for doing so might be implementing a proofing gallery for a client, or a private gallery of family photos.
By default, if you create a blog post with password protection it will wind up in your blog archives, on your main blog page and even in the Recent Posts widget. That is not ideal as it can confuse your website visitors as to why there is new content inaccessible to them. It would look something like this:
By installing the plugin, Hide Password Protected Content, you can automatically hide that content from showing in your blog feed or Recent Posts widget. Your site will now look like this:
The best part is this works for any password protected content and not just NextGEN Galleries.
It's worth noting that if you want granular control over indexing of your pages and posts as well, use Yoast SEO to prohibit a page or post from being indexed by search engines. If you do not, no need to worry as search engines cannot crawl a page or post that is password protected anyway.