However, speed isn't the only benefit. When it's easy and quick to search everything, one can often find lucky results that one wasn't expecting. For example, when I was searching for a message I received from a new client yesterday, I realized that I'd also corresponded with him in a previous job, several years ago. I'd forgotten about that and I suspect he had too. I was also presented with some web pages that mentioned his name, a saved PowerPoint deck authored by him, and his full contact details. All information that I had on my PC, but that I didn't know was there -- that's the point: global, indexed search allows one to find things one didn't know existed.
For the full benefit, the searching should be global -- i.e. the search tool should index everything on your PC, not just your email. Unfortunately, Eudora 7 only searches its own store, and therefore misses out on this serendipitous benefit.