I’m a bit of an outlier as I love as much information as possible. I’m the “manual guy” at work because I read more manuals than any other engineer in the company.My first computer, back in the last millennium, had a manual with the same problem as every other one I ever saw. It has absolutely everything there is to know in it. That gives them an out for any issue--hey! It's in the manual. The problem is that in information, theory, too much information is the same as too little information. What you need to know is a handful of drops lost in the flood of what you don't need to know.
Not only that, what you do need to know is not placed logically in a section titled Here's what you need to know. I am sure that is intentional, too for it prevents an attorney from claiming that doing so invited the reader to skip vital information. So as a new computer user, I had to ) figure out first what I needed to know, and 2) then I had to find that information scattered throughout the manual.
Years ago I bought an early Dive Right trimix computer online, and it did not have a manual with it. I got a PDF version online. Well, it turns out that the version I got was a PDF rough draft of the manual that was circulating with reviewer comments in the margins. Several comments expressed concerns about how the information might possibly open them up to liability.
I’ve found the best manuals, for any product, do indeed have a “here’s what you need to know” chapter, usually titled “getting started” or similar. This chapter gives you all the stuff you need to know for most cases. Importantly, it also links you to more detailed sections if something doesn’t make sense in the quick start section, or you simply want to know more about how it works.
I can, however, see why for liability reasons companies may not want this two-tiered approach, especially for human safety devices like dive computers. Even this seems solvable, like the disclaimers I’ve seen on quick start sections/manuals that say “this doesn’t cover everything, you need to read the entire manual before operation.”