I just realized that I don't know how to use hin and her. Beyond "woher kommst du?" I haven't learn to use them. As I understand, one can just juxtapose them to Ort prepositions:
(herüber, hinüber; rüber)
(heraus, hinaus; raus)
(herunter, hinunter; runter)
(herauf, hinauf; rauf)
usw.
where the first two entries stand for the written version, and the third entry here stands for the spoken version, either of hin- or her-. The latter prefix signals "towards the speaker", and the former points to the opposite direction, whenever it's possible to determine which is the speaker.
The question is: are hin and her optional? For example, is it the same to say
Gehen Sie bitte dort! or Bitte setzen Sie sich hier!
and
Gehen Sie bitte dorthin! or Bitte setzen Sie sich hierher!
?