Whatever floats your boat, but for me seeing 12 different class questlines is more entertaining that spending the same time mining and picking herbs.
The first post already stated the obvious:
There are other, equally viable or even more profitable ways of making gold.
This one is for the people who like alts or already have them or want to level them anyway for some other reason than just because their primary aim is goldfarming.
I levelled all the classes because I wanted to get all the class mounts. So I would have them anyway. Now the question is do I let them sit or do I try to make use of them. Guides like these help to see how to utilize alts. Around the time Blizzard started making Legion more alt friendly such guides started popping and several info helped me improve some things I didn't even think of (for example, how great are invasions for levelling, or the fact having a bodyguard with specific equipments actually adds up to a nice gold / OR gain).
If you don't have alts, and don't like to have them, what exactly is the deal? I don't get it. Every page has some poster coming over to say how much he dislikes the concept because he dislikes alts. If this content isn't for you, no biggie, it's not mandatory anyway.
If someone made a guide how to TSM snipe all day I probably wouldn't use it because it's super boring for me (while alts aren't), but I wouldn't deny usefulness of it to people for whom it's enjoyable.