Clean out location

[Kroman532]

General question. In my development all ranch style homes were built with clean out in basement one on main stack and one on floor.
All 2 stories have those plus one outside in front of house easy to see. Why was that? Just wondering

 

[Geofd]

Outside is a good place for a cleanout, if there is a stoppage you can open the yard clean out and snake from there if there are fixtures in the basement there should be a back water valve, all houses should have one outside it's just less messy if it is as to be opened