Worktop Joins... I'm curious?

Folks,
I'm not a tradesman, just a curious DIY'er...
With Kitchen worktops, when there are two bits of worktop to be joined, in a corner, why isn't a "standard" 45 degree mitre used? Why the "fancy" join that needs a jig?

I can see that this saves a bit of worktop being needed, (600mm or so), but other than that is there a good reason for NOT having a 45 degree join? Is is inherently weaker, or something else?

Thanks,

Regards,

Simsy