Create one file for all webservices instead of file for each web service

What about if i will create only one file for all functions of the web sevrices (is it bad for performance ?!) for example

if(commingJson['service']=="register"){
//here do work
}else if(commingJson['service']=="login"){
//here do work
}else if(commingJson['service']=="checkUser"){
//here do work
}else if(commingJson['service']=="deleteUser"){
//here do work
    }

and if it ok why people create file for each web service so in this case i need to to create 4 files one for select one for login , other for register also on ?!!