ADVANTAGES:
1) err, err, slightly more mpg (but more frequent oil changes and servicing initial cost more than cancel that out unless you do about 100,000 miles per year!)
2) err, err, ??? Anyone???
DISADVANTAGES
1) more expensive
2) heavier
3) slower (unless turboed but then you can turbo a petrol engine too! And then the diesel is last again...)
4) LESS torque size for size unless turboed (see 3) than petrol.
5) LESS power
6) Noisier
7) Tiring drone to drive
8) Tiring engine braking
9) Smelly fuel
10) Diesel on hands, feet, carpets, etc.when filling up
11) Engines wear faster due to: a) dirty oil faster due to soot getting past pistons which is abrasive b) Permenant WOT condition means the full 23 to 1 compression is forcing the pistons sideways in the bores and loading the crank madly even at idle!
12) Heavier battery needed and bigger electrical load on starting means starters and batteries last less well.
13) Less rpm band, more gearchanging so harder work!
14) Sounds like a truck especially when cold due in part to 11b
15) I dont like them!
16) need servicing twice as often due to 11a