Bro, I myself own Vitz now. The stock tires are 165/70/R14 with recommended TP of 34-36 psi (more in front than back). I haven't changed tires / rims yet, and maintaining OEM TP.
I have personally experienced that in case of my car, the stock tires / tires size; car performs best at 35 psi.
If you are using any tires sizes other than stock, then you will have to adjust everything yourself, by increasing or decreasing TP. Your vehicle has been designed and tested on 165/70/R14 at 34-36 psi for optimal performance. If you are going to play with tires / sizes, or TP, then for sure, performance, fuel efficiency, drive, ride comfort, handling, etc. Will get affected.