So, there are four different data to take into account when considering vertical metrics settings, and bear in mind that these were all originally defined in font formats in the context of Latin fonts and typography.
A. Simple ascender and descender values corresponding to the top of Latin /d and bottom of Latin /p that originated in Adobe’s Postscript Type 1 format. These do not have direct equivalents in TrueType/OpenType, but are often a starting point for calculating outwards to other metrics, especially for a font that contains Latin support, since this approach enables one to create a font that behaves similarly to other Latin fonts.
If a font contains Latin, I usually begin by measuring the height of /d and the depth of /p, and sum those distances to see how they relate to the overall body height, i.e. the total em height measured in units-per-em (UPM). That lets me know whether the Latin design is small or large on the body. Generally, I want the total height of ascender + descender to be close to the body height, because that means that e.g. at 12pt the typeface will be of similar size to other 12pt text.
B. Apple-specific vertical metrics in the hhea table of TT/OT fonts: ascender, descender, lineGap. These originate in Apple’s original TrueType specification, and are still used in Mac OS and iOS to determine default linespacing and text-to-frame distances. I’ll come back to these: I mention them first because they pre-date the OS/2 metrics.
C. Microsoft OS/2 table sTypoAscender, sTypoDescender, and sTypoLineGap (the Typo metrics); and
D. Microsoft OS/2 table usWinAscent and usWinDescent (the Win metrics).
I’ll discuss the OS/2 metrics together...