Originally Posted by narvik

It depends on several key factors. The mixed messages you've heard are likely all true, as it can vary a lot.

For instance, PEK has two main international terminals; T2 and T3. They are miles apart. Transferring I to I and having to change terminals also will necessitate entering China through immigration and customs. MCT is also double compared to staying in the same terminal (although IMO, neither MCT is really realistic).

For a simple I to I, not changing terminals, and having either no checked luggage or luggage not requiring to be picked up, a transfer is pretty straight forward, although still requires some checks. You won't be 'entering China' in those situations though.