Distances between objects
Photoshop has a useful feauture — it shows the distance between currently held object and adjacent one, when you hold Control.
(I coldn't capture these annotations on video, sadly).
AI just doesn't.
It can detect similar gaps between objects, show offset from current position, but not distances to neigbours.
And it even doesn't show offsets when you use snap to grid (with Smart guides on).
Please, make snaps great again.

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Leo commented
I use illustrator for a lot of infographic and technical illustrations and let me just tell you, how frustrated I am that it's obviously a very useful feature, it's already in XD, and yet it's still not in Ai.
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Payal Biswas commented
Like in Adobe XD, it would be great if we can check distance between elements clicking 'Alt'. Because checking distance by zooming in to the ruler and making it perfect is quite tiresome. Clicking 'Alt' as in XD makes it quite easier.
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Omar Guillermo commented
How to get this to the front page? It's kind of ridiculous that photoshop supports this and illustrator doesn't!