IMO its a wrong thing i think because the gap adjustment can be fairly critical, and if it is maladjusted the engine may run badly even though slight difference in gap may give too small and weak a spark to effectively ignite the fuel-air mixture, while a gap that is too wide might prevent a spark from firing at all. Either way, a spark which only intermittently fails to ignite the fuel-air mixture may not be noticeable directly, but will show up as a reduction in the engine's power and fuel efficiency.
Karthik.
First of all the ignition coils have a limited voltage which is easily capable of creating a spark even when the distance between the two electrodes(ground & center) is around 0.15mm max.But the gap which is set by the company & the service-centers/garage is somewhere between 0.6 to 0.8mm.So increasing or reducing the gap by 0.2mm or so does not lead to a situation of spark not falling at all and weak spark respectively as it is pretty negligible.It does not even adversely effect the engine.
The effects are as follows:-
1)Increase in the plug gap by 0.2mm than stock leads to more air-fuel mixture coming in contact with the spark & increasing the efficiency of the vehicle.Helps some one increase the average of their vehicle by 1 or 2km/l[.B]Excess[/B] gap may lead to problems in cold start or spark not falling.
2)Reducing the plug gap by 0.2mm than stock helps the car to perform better,useful for someone who drives at full throttle most of the times.
CONCLUSION :-
Therefor the spark plug gap i.e 0.6 to 0.8 is recommended keeping in mind that even changing it by + - 0.4mm wont lead to any of the problems you have mentioned.
Unless you ride/drive something like a sports car or bike.