In particular, TfL Go also has a focus on upcoming nearby departures rather than directions which Google Maps and Apple Maps prioritise. For anyone with some public transport familiarity, it’s quite nice being about to see your approximate position on a schematic tube/rail map or easily view nearby bus stops.
However, a friend who was briefly visiting London found this quite confusing as it wasn’t focused on navigation. Separately, I find the UI far too information-sparse for my taste compared to some other official apps (Zurich, Prague, etc.) which makes it somewhat inefficient to use, but perhaps this works for some.