To chop or to blend? Many dishes start off by finely chopping and then frying vegetables (usually onions, carrots, celery and maybe garlic) to get a good flavour base.

If you want to get the maximum flavour would it not be better to blend them all into a paste and then fry off the paste? (Assuming of course that they would cook away completely during the cooking anyway)
There's nothing stopping you blitzing a mirepoix in a food processor, but what tends to happen is that the onions especially release a lot of water which can prevent them, and the rest of the mix, browning nicely.

For this reason, a nice small dice is usually the best way to proceed.