Metafields earn their place when the data is structured, repeats across many products, and needs to be queried or displayed consistently — size charts, material composition, care instructions, custom specs that don't fit Shopify's default product model.
One-off content, marketing copy that changes often, or anything a non-technical team member needs to edit frequently is a bad fit — metafields live outside the normal content-editing flow and someone eventually has to go dig through the admin to find them.
If it needs to be queried programmatically or displayed the same way across 50+ products, metafield. If it's one page's worth of content a marketer will tweak next month, just put it in the page builder. Mixing the two is how themes become unmaintainable.