I wouldn't say that there's a recognized principle that proceeding by way of summary conviction.... It certainly doesn't make it easier to prove the offence, but if you proceed by indictment, it's a different set of procedures that apply, including the right to a jury trial, and it may go to a different level of court. If you proceed on summary conviction, the procedure can be quicker. Proving the offence would remain exactly the same, but the procedure might be simplified, and that's made available.
What we do here repeatedly from prosecution authorities across the country is that if you get a less serious case where you don't want to be seeking the highest possible penalty—maybe you're going to be seeking a penalty in the lower range—you go with the simpler procedure that avoids the potential for a jury trial and other procedural ramifications. For the less serious offences, the crowns do like the option of proceeding by way of summary conviction because it makes the trial process simpler, but it certainly doesn't make proving the case any simpler.