Were there ever any smaller sets, marketed as being combined to create a large official set? I recall a children's magazine running an article about how to take a few smaller sets to create a big space ship, but I am not sure if that was official.

Did LEGO ever create some smaller sets, but market them in a way to convince buyers to buy several other sets, so that they could be combined to create a single large set from those?
Some of the LEGO Star Wars Mini Building sets contained additional parts that could be combined to make an additional model.

For example, the additional parts from sets 4484, 4485, 4486 and 4487 could be combined to build a TIE Bomber.

This additional model could be built at the same time as the primary model; the primary model and additional models didn't share parts.

You could buy special packs that contained all 4 sets.