Toilet pans (bowls) are either S trap or P trap – this means the toilet is designed for the waste to connect to your plumbing pipes through the floor or behind through the wall.  In some circumstances the waste pipe might pass through the wall on the left or the right & toilet pans that accommodate these are called “skew” pans.  The simplest installation (lower cost installation) is where the new pan dimensions match the existing. Altering the waste pipe in the floor or a tiled wall can dramatically increase the price of your installation. Sometimes the dimensions of the toilet suites change and when you are installing a different type or brand, the footprint of where the pan sat on the floor &/or where the cistern is fastened to the wall & cosmetic touch ups (plaster wall patching, sanding painting or floor cleaning or surface repair) may be desired post installation but is not done by the plumber.