Sure - actually both. „Last seen“ and „last post“. Of course you can search for the user’s posts - but for privacy-oriented communities, it would be nice to either restrict visibility of the user details. Either site-wide, or maybe on a per-user basis like “I want to share my details with everyone registered users only no one”. So you present yourself either like this:
…or that:
If you post something, it’s clear that this is visible (unless you post in a hidden category). But if you only browse the site, we find it questionable that this data should be world-readable without a possibility to prevent it.