I was surprised when I first saw this. It's so simple, with no hard-to-get ingredients, that I would expect to see it on menus and at picnics and other al fresco dining opportunities. It seemed at first counterintuitive, but Tartar Sauce used to be used for many things beside fried fish, and this is just one simple example.
This is best in late spring and early summer when you can get fresh local asparagus. There are plenty of brands of commercial tartar sauce available on store shelves, or you can make your own.