I think the important issue is that if your outbound links are dofollow, then it's good practice to periodically monitor the sites that they point to. Domains get sold, website content that was honorable can turn shady, etc.
One of my clients monitors their outbound links quarterly. Out of 1,000 plus links, we usually find 2 or 3 every quarter that have turned to the dark side. One quarter we found 5. That could mean, over ten years unwatched, we might have had 10% links pointing to "bad" sites - malware, part of link pyramids, etc.