If you read older cookbooks, you'll notice a popular dish before about the 1960s, was "[something] in white sauce on toast." It could be all kinds of things -- mushrooms, chipped beef, boiled eggs, chicken livers, peas. Whatever.
I've tried this form of dish a few times and have noticed that, in general, unless the item being put into the sauce is very well-seasoned to begin with, this usually makes for a very bland dish... at least, if you use standard white bread for your toast.
As discussed before, using fancier breads can much improve certain basic foods. This is one of those. Mushrooms in White Sauce on Toast become very tasty when served on French Herb Bread. Eggs in White Sauce are nice served on Spinach Bread -- and so on.
X in White Sauce is nice because it allows you to use up just about any meat or vegetable you've got sitting around. The trick is in finding the right bread to compliment it.