Why I'm mostly not interest in exploring new fonts (on Unix)
Every so often, an enthusiasm for some new font or set of fonts goes around the corners of the Internet that I pay attention to. It's especially common for monospaced fonts (programmers seem to have a lot of opinions here), but people get enthused by proportional ones as well. I used to be reasonably interested in this area and customized my fonts and sometimes my font rendering, but these days I find that I generally take at most a cursory look at new fonts and tune out.
The first reason I tune out is limited Unicode glyph coverage. As
I found out when I dug into it,
xterm doesn't require your
primary font to have CJK glyphs, but as far
as I know it does require your font to have most anything else,
including Cyrillic, Arabic, and Hebrew glyphs, if you're not going
to see just 'glyph missing' boxes. I don't necessarily look at stuff
in these languages in my
xterms all that often, but it comes up
every so often and I'd like to have things available in any new font,
since I pretty much do currently.
(I have to admit that the most common place these character sets come up is when I'm looking at spam messages, email and otherwise.)
For proportional fonts, things are less clear to me. Firefox apparently still uses glyphs from multiple fonts as necessary (based on eg this bug), even with modern XFT/FreeType fonts. I believe that Gnome and probably KDE have some sort of system for this, which sometimes matters for programs like Liferea (syndication feeds) and Corebird (Twitter), but I have no idea how it all works or is controlled. If all of this works, it means that my nominal main proportional font wouldn't need complete glyph coverage, although I might have to do a bunch of configuration tweaking.
(Back in the pre-XFT days, Firefox used to have a quite complex and arcane system for finding glyphs to render, since X fonts often had very small coverage. If things went wrong this could produce rather bizarre results; Firefox was perfectly capable of switching fonts around in the middle of lines or words, even in nominally European text, if it decided that for some reason your primary font didn't have the necessary character and it had to fish it out from some other, very different font. All of this is fortunately behind us and I've mercifully forgotten most of the details.)
All of this matters because most alternate fonts don't have a very wide glyph coverage. This isn't surprising; drawing a lot of glyphs is a lot of work, and creating glyphs for non-Latin characters requires its own set of type design expertise in how those characters are supposed to look. In practice most artisanal new fonts are likely to be pretty much confined to Latin and near-Latin characters.
The bigger reason that I tune out these days is that standard Unix XFT fonts and font display are now pretty good. Back in the old pre-XFT days, X fonts (bitmapped or TrueType) were generally pretty limited and often not of particularly high quality, and rendering decisions could be questionable or oriented at hardware that you didn't have. This could make it very worthwhile to seek out an alternate font, because it could significantly improve your reading experience. I used an alternate bitmapped font in Firefox for years, and even after that stopped being a good idea I switched to an alternate TrueType font (one or the other is visible in this view of my desktop, although I no longer remember if it was the bitmapped 'Garamond' font or TTF Georgia).
The modern XFT world is much different. The current fonts that are mostly used and shipped by major desktop environments and Linux distributions are pretty well designed and have increasingly good glyph coverage (primarily this is DejaVu), and if you don't like them, there are alternates (eg Google's Noto). I've also come around to finding that the rendering decisions are generally good, which is a change from the past for me.
Given that the default fonts are already pretty good, the incremental improvement I might gain through fiddling around with my fonts doesn't appear to be worth the effort and the uncertainty. I could spend a lot of time tinkering, trying out various fonts, and basically wind up with something that was subtly worse because, to be honest, I don't know what I'm actually doing here (and I know enough to know that type design and typography is complex). So the easy path is just to use the defaults.
(This entry is sparked by reading vermaden's FreeBSD Desktop – Part 15 – Configuration – Fonts & Frameworks (via), and thinking about why I had no interest in doing something similar.)
Sidebar: Why Unix XFT fonts and font rendering got good
My impression is that part of it is simply the progress of time creating a slow but steady improvement, but a lot of it is that Unix/Linux font rendering became important enough that people spent money on it. Google obviously spent the money to develop Noto, but they're far from the only people. Sometimes this funding came explicitly, by commissioning font work and so on, and sometimes it came passively, where companies like Red Hat and Canonical hired people and had them spend (work) time on Unix font rendering.
(Android probably helped motivate Google and other parties here.)