You're supposed to read the abstract, preferably the bottom half first to see if there are conclusions there, then proceed to the conclusions if the abstract is insufficient. Once you're through with that, you can skim the introduction and decide if the paper is worth your attention.
Reading start to finish is only worth it if you're interested in the gory details, I'm usually not.
I was taught to read the abstract, then the conclusion, then look at the figures, and maybe dig into other sections if there's something that drew my interest.
Given the variety of responses here, I wonder if some of this is domain specific.
It depends also on what you want to get from the article. Usually I focus on the methods section to really understand what the paper did (usually I read experimental papers in cognitive science/neuroscience). I may read parts of the results, but hopefully they have figures that summarize them so I do not have to read much. I rarely read the conclusion section and in general I do not care much about how authors interpret their results, because people can make up anything and if one does not read the methods can get really mislead by the authors' biases.
It’s interesting how many different opinions there are in this thread! Perhaps it really varies by field.
I was reading mostly neuroscience papers when I was taught this method as an undergrad (though the details are a bit fuzzy these days).
I’d bet it also varies quite a bit with expertise/familiarity with the material. A newcomer will have a hard time understanding the methodology of a niche paper in neuroscience, for example, but the concepts communicated in the abstract and other summary sections are quite valuable.
I learned very quickly reading math papers that you should not get stuck staring at the formulas, read the rest first and let them explain the formulas.
I would not say it should be read start to finish, I often had to read over parts multiple times to understand it.
Reading start to finish is only worth it if you're interested in the gory details, I'm usually not.