Hmmm. wonder if I got something wrong?
We have a gas top and electric oven (Smeg, 90 cm). The oven has a variety of settings with fan and without, so that makes it convection, right?
Anyhow, I understood that I need the fan when the full-size pans or trays* are used to allow the hot air to circulate evenly (and, presumably, when I have loaded a full rack) but that otherwise it's not necessary.
If there was another purpose, I didn't know of it!
(I think this is a normal European thing: ovens come equipped with racks, of course, but also full-size cooking pans and shallow ("cookie") trays which extend from side to side inside the oven, using the same slides that the racks use.)