Seeing as there's an nLab page about creation of limits, I take it that at least some people think this is an important notion. There's also a discussion here about what the "correct" definition of this notion is. However, and maybe this is just my ignorance speaking, but I haven't actually found a reason to worry about this notion, so I basically just ignore it. I mean, okay, a diagram $D$ that lacks a limit in one category $\mathbf{C}$ might gain a limit in a category with more objects, or arrows, or both. More generally, given a functor $F : \mathbf{C} \rightarrow \mathbf{D}$, the composite $F \circ D$ might or might not have a limit, quite independently of whether or not $D$ does. But so what? I don't quite get what the notion "creation of limits" really teaches us.

Question.Can someone who finds this to be a helpful notion explain what they find helpful about it? Is there, for example, a theorem about creation of limits that's ubiquitous but impossible to see without this notion? Is there an important definition that can't be elegantly stated unless creation of limits is invoked? What's the point of this idea?

provethat limits in $\operatorname{\underline{Ab}}$ exist, but they would still exist if we didn't use that functor. In no way is $\operatorname{\underline{Ab}}$ a completion of $\operatorname{\underline{Set}}$ (as I'm sure you're aware). $\endgroup$ – R. van Dobben de Bruyn Sep 20 '18 at 21:49