I will answer my own meta question to explain how I made my decision.

Regarding the bounty, even one would be using own points and the decision is on whom had started that, one should also consider to evaluate if the to-be-awarded answer is actually "valued" by others to some extent.

I use the word "valued" to describe the uncertain hint or some shy acknowledgement by others based on the votes distribution and constructive comments. If the answer has the least votes and no other constructive comments, that will be more difficult to decide.

Looking at the example post (edited Mar 14 at 19:24):

I have to install Ubuntu on a PC and I saw I have to make a bootable LiveUSB from the Ubuntu iso file. However, I can't understand what's the technical difference between making a bootable LiveUSB with a program like Rufus, and copying a .iso file on a USB.
Why is not enough to copy it?

The question asked the difference between a Live USB created by the program and another one created by just copying. That is neither about how does PC turns on and boot the Live USB, nor about how does BIOS/UEFI handle a Live USB--these are indeed related but do not really answer the question.

As for the answers, many of them write like a commentary, a how-to, or a combination of both, which seemingly valid answers but not the real answer to the question.

Personally, I would consider sudodus' and Dmitry's answers are the real answers (to this meta-answered date). Both are good for different reasons that I could tell from my end-user experience, as follows.

• sudodus' answer is well-explained using less words. That contains conventional information for end-users to understand "there must be a bootloader" and some associated details with BIOS/UEFI systems and 32/64-bit ISO images.

• Dmitry's answer is short and concise. That contains sufficient information for end-users to understand Live USB has different layout from an ISO image, without complicating the matter with other technical information.

Between the two answers, sudodus' answer would have the upper hand:

• "There must be a bootloader" is essentially the short answer, and the remaining text are expanded from the first five words;

• The cloning tools and extracting tools: These are likely known to experienced users including myself, but somehow not well-explained by others (This explains how a Live USB may be created, given that "a program like Rufus" was noted by OP);

• "If you simply copy [...]" with external links: The reason is summarized in the last paragraph, then some links are provided for further reading (This repeats whatever explained from the beginning in least words possible that affirms the answer itself).

In terms of "valued" indicators:

• sudodus' answer has changed from +5/-1 (before) to +7/-1 (after). Down-vote reason is not known. At least one commentator appreciated this answer. No new comment.

• Dmitry's answer has changed from +1/0 (before) to +2/-1 (after). Down-vote reason is probably not worth the bounty compared to sudodus' answer, or might be the counter-vote that balances my earlier vote. No new comment.

My evaluation: sudodus' answer not only answers the question itself, but also written in a way that could guide the readers to understand how a bootable Live USB is different from an ISO image or a Live CD. In fact, this is the only answer that clearly described the way a Live USB may be created by cloning or extracting, in addition to the reason "why".

Based on my evaluation, sudodus' answer deserves the bounty.

P.S.: This meta answer is specific to the example post, and may not be applicable to other underappreciated posts.

P.P.S: The bounty is not awarded yet (This text will be amended later).