What is difference between suspending a computer and just walking away from it?

I've been looking at lots of web content about sleep, suspend, hibernate modes of a computer but I have not come across any discussion of this seemingly simple question: **What, if anything, is the difference between** 1. **just walking away from a linux computer**, running, let's say Ubuntu 22.4 LTS but it really could be any distro and version, and 2. **explicitly invoking the suspend command**, either from the command line or a gui? Both cases are supposed to enable you to come back to the computer later, click the mouse or type a key and "wake it up". ***If there is a difference, what is it? If there is no difference, why is the suspend command necessary?*** And by the way, is there a name for "just walking away"? Is that what "sleep" means? I find these terms thrown around without any precise definition of what each means. **Update: Why am I asking this?** **Most of the material I find in relation to the different forms of computer sleep, suspend, or hibernation assume that the main concern of anyone asking it is power consumption. This is not my concern.** **My concern is that when I leave my computer I can reliably come back to it and not need to reboot.** My concern is that I have purchased a fairly expensive laptop computer from Lenovo, with an nVidia graphics card (not going to get into the technical details here) that I cannot walk away from and reliably assume the system will wake up when I come back to it and press a key or make a mouse click. Sometimes it works, sometimes it doesn't. It seems that explicitly invoking suspend is a little more reliable, doesn't crash as often, but it is not 100% reliable, maybe 90%. On my previous computer, a 10-year old Lenovo laptop, I did not have to worry about any of this. ***Update 2: correcting original to mention "getting rid of Secure Boot under UEFI" rather than "getting rid of UEFI" as a prerequisite of achieving hibernation.*** Hibernation suggests itself as the most reliable way to achieve what I am after, but it is not currently available on my computer which uses Secure Boot under UEFI. So one option is disabling Secure Boot. I was reluctant to do it but that seems to be the way I have to go. **My main concern is reliability, not power consumption.**