Embassy staff-level employees for some countries travel on official passports, when they are sent abroad for posting in the diplomatic missions. Because they are not at the highest level (e.g. Ambassador or Consular Attache), so they are issued the official one......depending on countries sometimes these enable you to by-pass or not require some visas, such as transit, or short visits, etc.

I guess some sportsmen (for example athletes) would get them too for representing country officially.

A lot of benefits having those than the ordinary ones. They save a lot of hassle in many airports ^