In the early days of weighing, all scales were designed to be installed in deep concrete pits.  However, with the changes made in modular construction, Apollo Scales is now able to install pit scales in a more shallow pit allowing for less concrete and a little less expense.  

As shown in the table below, the biggest reason to choose a pit scale over a pitless scale is simply lack of space.  Pit scales will require less length as ramps are not necessary, however due to the pit they are more vulerable to rust and corrision from environmental exposure.