[solicode]

While I wouldn't say it's THAT significant, there is one other advantage to fixed-width fonts that I've experienced. Due to the fact that they align vertically, sometimes they expose mistakes if you're constructing data in a table-like fashion. Or when you have a bunch of copy/pasted lines that differ only in the parameter values. Like, "Hey wait a minute... this line is 1 char wider than the previous one. Oh, whoops, I fat-fingered something there".

I wish I had more specific examples and could quantify it better, but I know I've caught quite a few errors this way.

[koheripbal]

This exactly. Most recently I had a script that was calling functions with fixed width data sets (IDs, credit card numbers, birthdates, etc..), and typos were significantly easier to find due to the data and fonts both being fixed width.

[seanmcdirmid]

This is because we don’t have any decent rich formatting options available for code in a plain text file. You could totally find those errors in an excel spreadsheet, and excel doesn’t default to using fixed-width typewriter fonts.