Less co2 pollution and more efficiency. My car uses 8-10l of lpg and in my country lpg is twice as cheaper as petrol. So it's efficient almost as diesel engine is. 

I don't see any difference in performance, but overall I'm not expecting any performance from 100hp car. 

Cons are small tank (35litres) and no more space for spare tyre

Only disadvantage of lpg is when magnesium exsaut valves are on engine.After 50/60 k km thise valves are deforming because of higher combustioun temperature of lpg.

Advantages about 10% less CO2 half cost of gasoline and %25 cheaper than diesel per km.

No performance loses.Cleaner engine

we have two  Peugeot 406 2.2i 160hp both on lpg.
Both cars use omvl dream xxi LPG instalation, and uses about 1-1.5 liter more than gasoline.
also has about 20% less power and throttle response. But it's much cheaper than any diesel with similar perfomance and car size. 
No diesel sedan with 1500kg with 160hp can use under 6-7 liters per 100km, while our car uses 8.5-11 L/100km, depeding on driving style and LPG quallity
After removing engine head after 220.000km it's visible more carbon buildup on top of the piston, but non of carbon is seen on valves, beacuse first 3km or so car drives on gasoline. If you use LPG instal catch can, or once a week drive 20-30km on gasoline to clean the engine.
Our cars doesn't have valve saver fluid witch lubircate them, and never had problem with burining them. Japanese cars had lot of problems with LPG.