I have personally never flown a 172 with 40 deg flap - only thing I know is they are supposedly poor climbers on a g/a with 40 flap...
In general more flaps will allow you to land at a slower speed, giving less ground roll, less brake wear. On rough/soft surfaces the low speed gives you less chance of nosing over, etc.
The cons I can think about are
1) Reduced airspeeed -> reduced airspeed over control surfaces -> less control autority. Might be something to consider in a nasty crosswind.
2) The flaps themselves will also act like sails in a crosswind condition.
3) For practice, landing at different flap settings is good.