Vantaggi
You choose when to work so flexible hours, location etc. Occasionally you get documents that are already very well written and have bonuses due to short turnaround time - these don't take much time so the pay works out very well. Some documents are also quite interesting.
Svantaggi
The volume of work isn't guaranteed, so the times you might be available to work there may be no documents available. For documents written by non-native English speakers (especially PhD thesis chapters, scientific journal articles, etc.), which tend to be the majority of what you work on, you essentially have to re-write most of the text to ensure it makes sense - this takes far longer than the 2k words per hour rate they say experienced editors work at. I was doing it for about 11 months and was no where near completing difficult documents at that speed, so the pay works out extremely poorly per hour. You can't see the document beforehand so you don't know what the language will be like until you accept the document. Sometimes in the notes (before you accept) the admin will leave a note to say 'good level of English' - but there have been several instances where I accepted documents because they had this note and then they turned out to have quite poor language after the first couple of pages. There are opportunities for more regular/reliable work with business clients but these can be extremely tedious and again the volume of work available fluctuates.