The two expressions actually convey the same meaning, but in reality, native speakers prefer the latter for economic principle, i guess. Wo de is usually used when the speaker wants to emphasize a sense of belonging. In real communication, when wo de is followed by people, de is omitted because there is no need to emphasize that somebody belongs to the speaker. Wo in this case indicates relationship of human, while wo de indicates belonging.

Wo = I De = "Possesive" Ta de = His Wo De = My "Zhe shi wo baba" this is wrong grammar i think. we need to use "De" as possesive. #I'm not native chinese, Correct me if I wrong :D

When we talk about people or home related, "de" is optional, normally we drop it. eg: wo baba. but for non-living things like phone or water, "de" is required. eg: wo de shouji.