Some see it as food or a necessary evil to sustain a parasitic species.

While others, like myself-believe it to be like a drug they've been introduced and addicted to as a means of control by their Queen.

In the finale, it's been shown that too much love can be dangerous (and possibly even fatal) to them.

What do YOU think of their dependence on the chemical known as 'LOVE'?

My theory is that all magic in Equestria is heavily tied with emotions. In ponies especially. Changelings don't really drain emotions, just magic. Emotion just gives it flavour. However in case of ponies due to to how strongly their magic is tied with their emotional state it amplifies it's nutritional value.

1683674 That was a shield spell, not just love.

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W-verse mechanics is that emotions both are and generate astral energy; thus, changelings drain your soul of its power when they feed off you. This isn't a problem unless they really "sink their fangs in" so to speak, since you generate that stuff back up in a jiffy. However, this also means that as they charge up, their powers will get them increasingly moody and affected by whatever emotions they're currently storing; love is a base that can be transmuted into anything else, but for example rage is the base of most combat magic.

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In my stories, it's both food and power. They need regular food still, but need the energy from love (Or other positive emotions) to properly make use of it, otherwise they start to starve. It also powers their magic.

I's have to disagree with the idea that those episodes showed that "too much love" is dangerous to them. They were hit by a massive shield spell, not love.

For changelings I think its both food and power after all Queen Chrysalis was able to beat Princess Celestia with the love she had been feeding off of Shining Armor. Also there are different forms of love, so as food source I wouldn't be surprised if unhealthy forms of love such as obsession would have negative effects on changelings.

I see love as a tasty food for them.

Personally, there are a number of ways this could go, as emotions could either be food or another means to gain power. Choosing one of these two options will have staggering results, but the main question would be what would be the greater advantage?
I went with the food option, feeling it would add more need than greed in the show. Plus, it's a great motivator for a changeling to look for said emotions.
If we were to make emotions as food, that would mean a certain diet is needed. Love is seen as the best emotion by most, so lest say that love is a primary food source. Now, lets also say that other emotions are like other foods as well.
For a human, different foods will effect the body differently. So looking at it like that, I had changelings reflect this by having their personalities get altered slightly or change how they are able to do things.
A primary example would be magic. In my story, a ponies magic is heavily influenced by their emotions, but why? Well, I thought about it and thought that emotions could be a balancing point for harmony.
Now, if a changeling feeds on only emotions, but are able to use magic, that would mean their magic would be extramly pure, having little emotion to alter their magic. I found this a good explanation why all changeling magic is green, while pony magic has a assortment of colors.
Then I had another thought, what if feeding on one emotion would cause more effects for a changing? So thinking about this further, I figured that each emotion would have a different effect, and would tie in with a corresponding color.
Granted, this is all guess work and is completely made from the ground up as I don't have any solid information to use.
But I try to make it as reasonable as possible in my story. There is more to say I suppose, but I think I'll leave it up to you lot to decide if you wish to hear me ramble on.
As for the shield thing, I thought of it this way-- If a changeling can feed on love in a slightly passive manner, that means they have a certain intake. But Cadence, being an Alicorn of love, has magic that is tied into that. So, the way I see it, there would be too much love in the spell, making it impossible for a changeling to take it all in at once and there fore, get swatted away.