Hey Ron,
The Snapshot just "remembers" the position of a components. It's like a polaroid camera, capturing a moment.
Snapshots capture and store positional information about components but do not otherwise enforce any positional constraints or impact the available degrees of freedom for a component.
If you've ever seen the "Some Components Have Been Moved" warning message during the creation of a Joint, it's because there is a pending snapshot that has not been captured in the timeline. Fusion 360 is just warning you that it will create a snapshot if you select Continue or revert to the original position if you select Revert.
Whenever you move a component (not a body), you'll see the "Position" panel appear on the right side of the ribbon. You can choose to save a snapshot of the new position or revert back to the old position after a move.
An awesome benefit of snapshots is that they can be used to create Positional Modeling features in your design.
Around the 5 minute mark in the below youtube video, this is demonstrated in depth.
https://www.youtube.com/watch?v=0Ep8NsC-jYU
I hope this helps clarify a bit more about Snapshots. Let me know if you have any questions, I'm happy to help.
Thanks,
Nathan Chandler
Principal Specialist