Callebaut callets vs. block?

Low quality chocolate chips often have additives in them that help them keep shape and shelf life, that's why they're not recommended. Callebaut callets are pure 100% chocolate according to Callebaut. I'd use them anywhere for bar or chips with great results. They might not come out of the oven looking exactly like a traditional chocolate chip cookie (for example) but they should taste fantastic!

I feel some of the answers here are too categorical. They fail to distinguish between the chocolate format and the blend. There is no one-to-one relationship between the format (e.g., chip/wafer/block) and the blend (ingredients, esp. the quantity and type of fat).

Couverture-quality chocolate, used for confections and ganaches, will typically only use cocoa butter as the fat. In particular, premium chocolate for coating ("couverture" = blanket, covering, coating) relies on cocoa butter for tempering. Such chocolate can be provided in any format, including chips.

Chocolate chips specifically intended for baking will have less cocoa butter than couverture, or even no cocoa butter, substituting other fats. This isn't necessarily a quality issue. Couverture-quality chips melt more easily and with greater fluidity than you may want for baking; the melting chocolate may spread out too much in the batter during baking. Chips specifically for baking use a different fat blend so that they keep their integrity better during baking. Of course, some manufacturers may use an inferior blend to keep costs low, sacrificing quality. But even premium manufacturers often use different blends for baking chips vs. chocolate intended for confections.

"Callet" is a button- or wafer-shaped format used by Callebaut and other manufacturers, to make their couverture chocolates easier to dispense and measure (vs. a block format). But manufacturers produce high-quality chocolate (couverture-quality, and for baking) in diverse formats, including in chips just like Tollhouse morsels. For example, Guittard's Akoma chocolate chips are in the standard chip format for baking, but have only cocoa butter as the fat (and taste a lot better than, say, Tollhouse, Hersheys, or Bakers chips—for my tastes, of course). Michel Cluizel is an example of a fine-quality French chocolate brand (with a price to match) that sells couverture in a regular chip format.

Speaking for myself, I often use some couverture-quality chips or wafers (callets, buttons) when I bake cookies or blondies. I don't care that they spread more in the batter; I kind of like that, in fact! That said, I do also keep baking chips in stock, and I tend to mix them and couverture chips and wafers when I bake. This is partly to control expense, but also there are some baking chips I do like a lot. I much prefer Ghirardelli and Guittard baking chips to the standard store brands (Tollhouse, Hershey, Bakers). Guittard in particular is a US chocolate manufacturer that is very well known for their couverture-quality chocolate for confections (sold in wafers and blocks); but they also produce chips specifically for baking.

We use these for our homemade truffles, peppermint bark, and other candies. They are as good as any bar with a bonus-no chopping! IMO, that is their big advantage.

The idea of not substituting chocolate chips for chocolate is based on what the other answers say: that chocolate chips have different ingredients (usually a substituted fat in addition to or instead of cocoa butter) than regular eating chocolate.

That is true for many brands.

However, some brands of chocolate sell callets, drops, or chips which are exactly the same formula as their bar chocolate. One such brand available in grocery stores is Ghirardelli. Caullubet is another, although not a grocery store brand. The "disks" from many quality chocolate makers such as Del Rey are also their regular quality chocolate. The form factor is to facilitate melting.

If you know the chocolate is real chocolate, you can use it for any application suitable for real chocolate. Of course, its good to read the label, and know the cocoa percentage and so on for taste, but real chocolate is real chocolate.

Yum.

Cooking chocolate has additives (such as vegetable fats) designed to make the chocolate more "chocolate" like AFTER baking

Regular chocolate tend to go dull, and stay soft and even sticky after baking, so may not be ideal depending on what you are making

Most people can't taste the difference once baked inside a product e.g. chocolate chip cookie

Save your good chocolate for eating straight!