What advantages would a "mix'n'match" approach like this have over something unified like Prototype (which, as far as I can tell, includes implementations of al

What advantages would a "mix'n'match" approach like this have over something unified like Prototype (which, as far as I can tell, includes implementations of all the parts you are using)? I have found Prototype much better for a "web-app" framework - I can build up complex controls and effects with the "OOP"/Inheritance framework, and I have access to all the functional tools I'm used to from Ruby. JQuery, on the other hand, has always felt "lighter" - really great for a quick Carousel control on a marketing site, or a pop-up effect or something like that, but it quickly turns into spaghetti with anything more complex. I'd be interested in other people's views on this split, especially people with experience using a whole toolset like yourself.