Maggots are a good bait to loose feed with and so much the better if used over a bed of groundbait. The one thing that I do know is that it makes the maggots wiggle more. It would make us wiggle too if we were dropped into a giant tin of curry powder. So rather than the taste and the smell it could be the extra movement that attracts the fish, but perhaps we shouldn't analyse things too deeply, but just accept it as an improvement. Now having examined baits extensively, I am beginning to feel like a modern carp angler who believes the most important aspect of fishing is the bait, when in fact it is not.
Location is far more important.
It doesn't matter what bait you have, or how good it is, if you are not in the right place you will not catch anything and that goes for all types of fishing. I must agree, anglers who fish long sessions have more chance of being in the right place at sometime or another, but anglers who only fish an evening, or a day have got to get it right fairly quickly. It is worth spending some time watching for movements of perch for they often reveal themselves as they attack a shoal of small fish, a dozen or more small fish spraying out on the surface in all directions is usually a sign that a perch is on the rampage. It could be a pike but the more fish that jump out at a time, the more likely it is to be perch. The margins can be good places, especially if there is an undercut bank, or the bank is sheer.