Is there a particular reason as to why slab edges always seem to be chamfered?

Each flag has been designed with a shamfer on the edge for installation reason. Indians stand stone the shamfer are opposite to concrete slab this is for when you fill the joint it protects the edge of flag and bends the sides. Concrete flag shamfer are positioned v up this is for many reason and check fitting details. it to helps compact joints if any movement also gives the finish required joint finish and also allows for water to run off the flag I'm sure if you contact the manufacturer they will give there reason for design

It’s for pointing purposes. Not so important of late as there’s lots of other grouts and mixes available BUT if you grout the same day as you lay it’s MUCH stronger and less likely to ever fail as it’s locked as one with the mix the slabs are laid on! Never a good idea to grout next day