Indeed, what units are convenient depends on context. Metric/SI is set up so that most of the un-prefixed units are a convenient size on human scale. But doing

Indeed, what units are convenient depends on context. Metric/SI is set up so that most of the un-prefixed units are a convenient size on human scale. But doing this means that some derived units will have values that are not human scale (like the Pascal, atmospheric pressure is ~100000 pascal). The nice thing about SI is that they subdivide easily in powers of ten, so even if the Pascal is inconvenient in our day-to-day lives it's easy to talk in kPa as 1000 Pa. This is contrasted with something like Imperial units, where every division of e.g. distance is supposed to be roughly based on some physical object. That's why you end up with 12 in/ft, 5280 ft/mi etc. Or alternatively you end up with metric-imperial hybrid units like the kilopound. Not to mention, what units are convenient vary depending on what you do. For instance one of the SI alternative units for energy is the electron volt (eV), the work done to move an electron through a 1 volt potential. This is a tiny amount of energy on human scale- a common analogy is that 1 MeV (10^6 eV) is enough energy to make a single grain of sand twitch a little bit. But, if you're a nuclear physicist (or maybe a chemist) then eV are typically much more convenient than say Joules.