What are they for? Both are a list of free tags. Why not having just one field.
Real case to show the confusion, at Purchase orders: Change source for region of desti... - SAP Community:
Links to definitions:
What are labels?
Labels are used within the SAP Community to help categorize content in discussions, blogs, Q&As, and knowledge bases
Labels enable you to categorize the content you write based on the themes or content in the article. For example, you might apply labels like "Innovation Alert", "Localization", or "Configuration".
Unlike tags, labels are created by the Admin and typically controlled for consistency.
Some Groups have a pre-defined list of labels, depending on the purpose and setup of the Group. In which case authors can choose/apply labels from the pre-defined list in the Group in which the article appears. Some Groups allow members to add their own labels. Tags are more free-form and can be created by any author - therefore anyone writing content.
It is also possible to subscribe to a label to get notifications of new content associated with this label. See the section: How do I subscribe to a label.
What is a tag?
A tag is a single keyword or phrase that describes the topic, theme, or subject of a post. You can add as many tags as you want and so can other SAP Community members. For example, in a post about a SAP S/4HANA Cloud, you might add these tags: Implementation, guidance.
Be sure to use commas between tags.