Should prepositions be repeated?

Answer 1

I cannot imagine a reason for that, unless in combination with a noun or verb that has the same prefix.

Example: Vor seiner Abreise in den Urlaub musste der Steuerberater unbedingt einen Termin mit einem Klienten vorziehen, der in die Zeit seiner Abwesenheit gefallen wäre.

Answer 2

The implementation of a German preposition marks the beginning of that prepositional phrase, and everything that follows it is part of that prepositional phrase. No prepositions need to be repeated.