It depends.
Air Canada's flight to Red Deer were rumoured to be anchored by 3 Super Elite flyers plus the members of Parliament. The flight kept them loyal, and otherwise was a wash. A net benefit. Those were Beech 1900-Ds though, 17 passengers.
Q400s are just too big for lots of flights. Air Canada has ordered 30 30 seat ES-30s (below) and if they're delivered, they'll be able to boost frequency on lots of routes where frequency can induce demand (I fly often these days between Vancouver and Kamloops-before going all Q400 Kamloops had double the frequency and locals bemoan it).
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