Viewers thought of them as that, and in popular culture that is what cue dots are remembered as today, especially by the Map Men, but technically that is not what cue dots were.

They were a way for the network to cue the regions for when to insert their regional content. It was not necessarily advertisements. And for programmes that were already regional, there was no need for cues from the network for when to run advertisements.

With digital playout, such things became no longer in-band.