if putting "Custom"
meta description for EVERY page of site, is harmful for SEO?
(for example, summary of each article)
And Google will show them on SERPs?
Your meta description should describe what the page is about, not what the website is about .
If you have website about wood work, your meta data shouldn't be the same on all pages. If you had a page about a band saw, your meta description should reflect that it's about a band saw.
So no, it's not harmful, it will tell the users on the SERP exactly what the page is about.
Google will decide what it thinks best to show as the description but in most cases at least some portion of the description will be shown.
Each page should have valuable content, a unique title, and a unique description. Your website should be mobile friendly. Having a legitimate meta description that is unique to that particular page cannot hurt SEO.