The concern is straightforward: an agent representing both sides has a harder time negotiating hard on price and terms for you specifically, since pushing too hard against the buyer works against the same agent's other client. Written consent is required precisely because this conflict is real, not theoretical.
If you are comfortable with a designated representation arrangement, ask exactly how the brokerage separates advice to each side internally, and confirm in writing under Saskatchewan Real Estate Commission rules that either party can withdraw consent within 24 hours if it feels unbalanced as negotiations proceed.
You are allowed to simply say no and ask for a different agent to represent the buyer instead. Get your hand-reviewed valuation from Joel Dyck.