>A lot of people rely on the implicit /persistent:y that gets applied when they interactively map network drive letters in, say, Windows Explorer. Most of the time that makes mappings persist across logons/boots but it's not 100% reliable, and every failure generates a support incident. Automatically or manually run scripts can work around this but are often not used.
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>Depending on client hardware you can also run into some subtle and hard to debug problems. For example, I've seen laptops with all-in-one memory card readers where each of 5 card slots gets its own hardware drive letter e.g. E: through I: inclusive. If you have any kind of script running NET USE F: \\SomeHost\SomeShare /persistent:y, then that command will fail, either silently or with an error the end user may not notice or understand. This gives the user an F: drive with nothing on it (all their files are gone!), so they have a heart attack and support gets a priority 1 elevated incident to handle.
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>In short, there is one legitimate reason to use mapped drive letters, but they are overused or abused in almost all other scenarios.

The other legitimate reason is that the persistent mapping is a way to memorize the location. While typing \\SRV0x002101\apps\myapp may not be too hard or too long, distinguishing it from \\SRV1X002011\apts\myapt in an environment where there are 12 other similarly named servers with similarly consistently named shares is near impossible. Or we could say it's possible but exhausting and with at least one accident per person per week almost guaranteed.

That's because there's probably no API for MRU locations per app, specially not in the getFile() dialog. The "Recently used" thingy was an attempt in the right direction, except that it 1) created .lnk files instead of maintaining a simple list; 2) memorized only files opened from WExplorer but not from inside the apps, even though the getfile() and similar dialogs use it, 3) memorized them per user, not per app. This didn't help - even in W2008 and I think W2012 I still see the MRU list in the FExplorer (renamed from one misnomer to the next one) being near as useless, it has shorter memory than I.

I know, there's a simple way to memorize network locations - stuff them into environment variables - but that involves messing with startup scripts, and you can't just "Modify Command %temp%\blabla.txt", but you can paste "%temp%\blabla.txt" in the filename combo or %temp% in the address combo. Still, I'd rather see a list of favorite locations in the file open dialog. Gimp maintains one interntally - which is nice, but I'd like to see that available to all apps.