Well, Snap to Point, as the name implies, was designed to snap anything you drag to a point — and nothing else.

You can also drag an edge, or just grab an object by its fill... what’s important is that it happens at the POSITION of the CURSOR. It means if you grab BY the point, having the 'white square with the dot' indicator, (with Smart Guides disabled) — it will be snapped precisely... but if you grab by the segment or fill (the marker would be the 'black square') — Ai would use the position of the cursor. And here’s where the tolerance kicks in... Ai allows us to grab the shape/line/whatever not precisely (obviously, since the screen is having finite resolution), and lands the dragged artwork within the same tolerance! Grab a line by the middle somewhere, aim at a point (the cursor would change to the 'white arrow', as with Direct Selection, to signal the snap target), release, zoom in and look.
So, Snap to Point works best when you grab BY a POINT, and snap TO a POINT.

This is the main source of our complaints with this snap mode — Snap to Point knows nothing about PATHS. Only P O I N T S.
This is what Smart Guides do: this mode knows about paths, intersections, etc. But these can be noisy (still, after the recent reworking).
So we often disable Smart Guides , using Snap to Point instead, forgetting or never knowing what the mode does.
Therefore your chart. You charted it correctly, and the road to this comprehension is hardly short.

Then there’s another secret snapping-ish option...
Read more about it here: http://illustrator.uservoice.com/forums/601447/suggestions/32318284

Does it make any sense?

Chart

Hi Egor. I have both snap to point and smart guides on. Currently I'm unable to reproduce the same issues as the videos I posted. I'm able to see where two objects are snapping when the magenta line appears when two edges have snapped to a common point/edge. I've tried various ways of copying and moving objects to snap to other objects, including object to guides, and so far it is working as expected.

I tried snapping edges of simple vector shapes as well as bitmaps, and the edges and point of the bounding boxes snap together okay.

However, I noticed that smart guides by itself seems to handle snapping functionality when turned on. Snap to point turned on or off seems to make no difference.

But when I have smart guides off, snap to point only works when bringing two points together. It still doesn't work when you bring a point to an edge.

I'm using Illustrator on an Apple M4 Pro, Sequoia 15.5. AI version 30.1

If you still need me to upload the Preferences folder, I can do that.

Ronald, Christopher, when it starts happening, does it affect everything, in all documents, with a simple case of rectangles?
When it happens again — can you please locate the Preferences folder (locations are mentioned here: https://helpx.adobe.com/uk/illustrator/using/setting-preferences.html), zip it (for the team to study), and share a link to the archive here, along with your full OS and hardware specs? Even though the test file might seem 'it’s like a simple document!' — share it as well. The problem is reproducibility. It behaves just fine for many, but for some of us... the combinations of factors differ.

This is the same experience for me on the latest version 30.1
However, it seems to work intermittently. If I reset preferences, snapping may work for a while, but the guides won't display OR the guides will display but the snapping doesn't work (even with Snap to Point turned one, and Smart Guides turned on).