That tag is something that usually gets misused. For example, I have seen best-practices used for questions on how to design something that lacked sufficient information or used by someone who wanted free consulting. The tag also gets misused to try to solicit opinion-based answers or off-topic recommendations.
Questions tagged with best-practices asking something like:
Should the NOC be connected to a P or PE router in a good design? If
the NOC will be connected to a PE router, it may be unable to reach
the P routers.
are simply too broad and lead to opinion-based answers. There would need to be a lot more detail explaining the network to even start to answer the question.
The question to which you refer could have attracted many conflicting opinion-based answers, possibly creating a flame war, even if answered and accepted with, "no best practice exists," as you suggested. That is something each company would need to decide on its own, based on its site requirements. There are sites that may have three people and a printer with no room for growth, and there are sites with hundreds or thousands of users that constantly move around (moving to a different network closet and switch), or grow and shrink as a market expands and contracts (think about the home mortgage market, sensitive to interest rates, that hires many people as refinancing grows, then lays them off as refinancing shrinks).
There are legitimate uses of the tag. A proper use would be where there is a vendor that publishes best practices. There are also best practices enshrined in RFCs.
There are best practices recommended to prevent potential problems. For example, to prevent STP problems, Cisco recommends that a VLAN not extend to more than one access switch (an access switch could have multiple VLANs, but those VLANs would not be on any other access switch), and access switches should only connect to distribution switches, not other access switches.
There are also best practices dealing with security. For example, not using the Default VLAN (VLAN 1) and not using Native VLANs on trunks, disabling Proxy ARP, and never allowing Directed Broadcast.
If you search NE for
best practice (not the tag), you will get answers that should legitimately use the tag, but are not using it. You will also find some questions tagged that way that should really be closed as too broad and have conflicting, opinion-based answers, but they were from the early days of the site, while standards were still being defined. There are also good questions with good answers that should be tagged that way.
Nobody, even moderators, can delete a tag. The only way to get rid of the tag is to edit every question using the tag to remove to remove the tag from each question, then wait for it to be automatically removed by the system (I think 72 hours).
A tag description can be updated by anyone, even you, to clarify when it is appropriate to use it, and when it is not appropriate to use it. (Users below a 5000 reputation will have tag description changes placed in a review queue for approval.) Unfortunately, many people simply look at the tag name without reading the description. That is a problem on all SE sites.