Knowing some of the changes Latin went through on its way to Spanish helped me at least once. I would use (inflict?) my Spanish on the kind folks at a nearby Mexican restaurant, and when I ordered a fajita quesadilla, the server asked me if I wanted "hongo". I thought for a second, recalled the "f" -> "h" transition (e.g. ferrum -> hierro, facere -> hacer) and "u" to "o"... aha! fungus! Why yes, I do want mushrooms on my fajita quesadilla.