I worked in IBM Hursley every working day for several years - and I still go there a few times each month.
For all that time, the cleaning staff employed a remarkably effective system: whenever one "restroom facility" was being cleaned, all the nearest ones would be free. That is: even though there were multiple cleaners, they managed never to clean two adjacent washrooms at the same time.
That way, if your 'favourite' one was closed for cleaning, you could walk to any other one and be sure it would be free.
I noticed how useful this system was when I was on my last project (at a telco in East Anglia). They did not employ this system and one would regularly have to try three or four different parts of the site before you could find an open washroom (or just wait until they were done... but I'm impatient)
You can imagine my shock, therefore, when I was in Hursley last week and the same fate had befallen that site: two adjacent washrooms were being cleaned at the same time.
This has completely shattered my assumption of good planning... perhaps the apparent efficiency of my first three years at IBM was just good luck!