breastfeeding is always about food and about comfort. you cannot separate the 2.
while a 3yo may not need the nutritional value of breastmilk in the UK, surely the fats, proteins, carbs, minerals and vitamins etc in breastmilk is as nutritionally valuable to his daily irrespective of why it is given. (comfort or nutrtion).
Likewise, I would not tell a 3 or a 30 yo that they ought not have that banana because he already has a balanced diet. that the banana does not add any thing to his diet and actually that he ought not eat that banana for, heaven forbid, comfort.
the occasional banana may be more nutritionally significant because the potassium in it may be something which is a bit lacking in his normal diet. ergo the occasional feed.
what if the toddler is going slowly into meltdown because her blood sugar is a bit low or it may be a bit past nap time and you can't get home or to the car just yet (as I vividly recall one day with dd1 when we were in denizens of Ikea with no snacks on hand. that) A quick feed addresses the sugar need (nutrition) and the diverts the tantrum (comfort). Sometimes toddlers are whingy, angry, confused outwardly to us and a breastfeed can address both at the same time instead of having a banana hurled back at me (in Ikea) by a toddler who doesn't quite understand that food is what it needs.
In time a toddler who has his needs for comfort met compassionately outgrows that need and is secure in his independence to move on to the next stage of life.
And why should we have to put conditions on how that child is comforted? Letting a child cry for a few days may work for a large percentage of children or rather spare the drama. This phase of their lives is so short. I've come to see it as a journey for my family which evolves into another one all the time. Along the way I am learning the depths of my compassion and humanity which I could not fathom before. The good and the bad days of breastfeeding is a small but significant part of that journey. My children teach me more about myself all the time.
Soon they will be shutting my front door behind them as they head off on gap year. Why hurry it up? I don't want them to leave home at 14.