I add Seachem Prime to all the water i use for water changes.
Leaving municipal supply water overnight used to be the traditional method of getting rid of chlorine in this hobby, however, most municipalties (including Toronto) now use a combination of Chlorine and Ammonia (which forms Chloramine). Chloramine does not dissipate as readily, according to some claims.
Water conditioners also contain other beneficial components (for example, stuff that is supposed to help fish with their slime coats etc), and, a $20 bottle of prime lasts quite a while (in my case).
For me, even if none of the municipal water chemical dissipation rates / product marketing claims are true, it comes down to two things...peace of mind, and the convenience to do impromptu water changes.
$20 over a span of 6 months is a more than a fair tradeoff for that, in my humble opinion.
“Logic will get you from A to B. Imagination will take you everywhere.”
― Albert Einstein