What are the REASONS for wanting no childs or waiting more than 3 years?

Exactly. The way people are talking here, it sounds like you are some saint when you reproduce. Not true. Too many people have children for the following reasons:

-boredom
-girls want a toy to cuddle, and a being to call their very own
-hope for a better relationship with their spouse/partner
-everyone else is doing it
-greed
-vanity
-accident

Others have children because it is the right time, they are ready (according to their own perception, or Allah's). But don't tell me Jamie Lynn Spears is a better woman than I am, just because the condom broke.