Main advantages of cargo are :
1.No pax ,therefore no air rage or other pax related problems.
2.In my job at least ,plenty of time off as night freight mainly is a Mon - Thur night operation .Finish work Friday morning back Monday night.
3.More relaxed working environment.
Main disadvantages :
1.Rare to get discount travel to the same extent as pax operations.
2.Mostly old ,tired aircraft.No B777 or A340 freighters ,a few B747-400 but these are rare.
3.Mostly night ,however suits some people ,me included.ATC delays rare ,radio very quiet ,lower temperatures (Australia can be extreamly hot in summer),usually get direct routing.
4.No glamour at all in the freight shed at 3.00 am.
5.People asking you if you are allowed to fly passengers ,or are restricted to cargo.
6.Tend to be more dodgy freight operations than pax ones as the pax ones are jumped on very quickly by the Civil Aviation Authority.
I'm sure other pilots could add to the list and although there seem to be more disadvantages I'll take freight over pax any day.