in the dry wider tyres will grip better. in the wet if they are too wide they are more likely to aquaplane as they have to pump out more water.
more grip isn't always a good thing though. the trade off with grip is resistance. a wider tyre has more resistance, so at higher speed wider tyres can reduce acceleration and top speed.
for the drags you want as grippy (not necessarilly the widest) tyre you can get as the launch is all about grip. a supper tacky 225 will grip better than a rock hard 305. but then once you are up and going and have no problems with wheelspin you want a skinny tyre again to reduce resistance. and on the front you would want as skinny as possible to reduce rolling resistance.
for track work you want grip all round so you even up the tyre sizes since the front needs grip to stop the brakes locking (a gbetter tyre will let you brake latter than bigger breaks (unless you are unable to lock a wheel with your current brakes), as bigger brakes will make it easier to lock a brake, but better grip means the road will keep forcing the tyre to keep rotating under a higher breaking force) and give you turn in without understeer.
if you got 2 tyres of the same compound, 1 a 225 and the other a 245 then the 245 would have more grip as they are the same compound, but if you get a 235 semi slick and a 265 cheap chinese tyre the semi slick will be much better.