Well, I can't think of any times where I needed to do more than 3 joins either. However, I find it helps me enormously when I can look at all of my tables and the joins between them. (I have had databases with 20-30 tables, and that is too unwieldy to memorize.)
And back to an earlier point...
I am working with someone else's database design, and so for me, the quickest way to get up to speed is to see an ERD. (If I had created things from scratch, I could likely do things - more easily - in my head as well.)
Hoping someone out there has used an open-source tool, that is a stable project, that does ERD's (including Reverse Engineering), and was happy with the tool.
(I hate to admit it, but MS Access's "Relationship Window" does a great job considering how basic it is.)