Even though Transport Canada does not require micro-drone pilots to register their <250g drone nor obtain a pilot certificate, are there any benefits or drawbacks from doing so voluntarily?

https://tc.canada.ca/en/aviation/drone-safety/find-your-category-drone-operation#micro-drones

I do not see a need to register <250 gram drones. The web site that you posted wants your credit card. The only benefit they offer is your lost drone may be returned to you by the required registration number on your drone. Just write your phone number on it.