What design limitations does a higher-than-average resistance trace impose?
1/2 oz copper (about the lightest typically used) has a resistance of approximately 1m\$\Omega\$/\$\square\$, so it's more than an order of magnitude worse, and about 50x worse than the 2-oz copper typically used for power circuits. 

You'd have to take that into account for power circuits, for analog circuits and for digital circuits that draw a lot of power. If you're just flashing LEDs with a microcontroller.. maybe okay. A 10 mil trace 3" long would have a resistance of 3.6 ohms, so at 50mA it would drop almost 0.2V.