The confusion comes from the two numbers moving in the same direction most of the time. Saskatchewan taxes residential property on 80 percent of assessed value, so a lower assessment does lower your carrying cost while the home sits on the market, which matters on a tight timeline, but it has no bearing on what a buyer will pay at closing.
An appeal can still be worth filing if your assessment is genuinely out of line with comparable Brighton properties, since it lowers your holding cost for every month the home is listed. Just do not expect a smaller tax bill to move your list price, and do not let a high assessment talk you into overpricing either.
The number that actually sets your price is a comparative market analysis built from what similar Brighton homes have recently sold for, adjusted for your home's real condition and improvements. Get your hand-reviewed valuation from Joel Dyck.