Data Pull vs. Push OOP Approach

Question

When I design my system from scratch, I often face a dilemma whether my object should push information into another objects OR whether the objects should

Answer 1

@kamil-tomsik What do you think on a client server model, where you have hundreds of client who are observers, but they don't need same data, so if you push you have to send them all the data you want to share, but some of them, don't need it. Isn't it slow down the communication?