The dative names the person or thing concerned ("for", "to", "in the eyes of"), and with est it names the owner.
Reference and advantage, "for, in relation to": parti unicuique bonum "good for each part"; tibi prope confecta est "is almost over for you", that is "your life is almost over". It is often best rendered with a possessive.
With adjectives of likeness, fitness, equality and nearness (similis, aequalis, utilis, amicus, consentaneus, congener): omnibus aequale "equal for all", naturae consentaneum "in accordance with nature".
Possession: est + dative means "have": est mihi liber "I have a book", literally "there is a book for me". The dative is the owner, the nominative the thing owned.
The dative also names the doer with a gerundive of obligation: mihi agendum est "I must act".