Definite article vs. possessive pronoun when indicating actions

Question

What’s the difference between using a definite article and a possessive pronoun to indicate actions (and possibly other things, if applicable)? For example, is there any difference between using die and seine in the following sentence:

Er sah auf seine linke Hand.

Where are the uses similar and where do they differ? Which is more common? What are the nuances of using each?

Answer 1

Really necessary is the possessive pronoun only, when other persons are on the scene for disambiguation - whose hand did he look at. (Dolls etc. could also qualify.) But there is no harm using it in the other cases too, actually I consider this as more naturally.