Made a dismaying discovery this week that has caused many headaches at our shop. If a team member opens a Sketch file but doesn't have one or more fonts, stand-in fonts are used to render the text. All well and good, that's how it should work.
The problem arises when the file is autosaved. Sketch bakes-in the replacement font! So if all the text in a design is Meta Serif, for example, and one front-end dev opens that file but doesn't have Meta Serif, doesn't touch any art but simply switches from one page to another, that triggers an autosave. The stand-in font (usually Lucida Grande, it seems) is saved and later if someone who does have Meta Serif installed opens the file, it will be Lucida Grande throughout. Adobe products, by contrast, show a stand-in font but don't make any changes to the specified font on save.
This has caused a huge amount of work for me over the last week. At minimum I have to go into Dropbox and roll back versions. At worst, I didn't catch it at first and made changes to the damaged file, at which point it's too late to simply roll back, and I have to repair the file manually.
Still waiting on feedback from Bohemian (sent a bug request last week and tweeted to them today). I'm posting this here to warn everyone to watch out for this behavior, as it can be incredibly time-consuming to manually fix things if you don't catch it before changes are made.