I am running both outputs of this https://www.pololu.com/catalog/product/713 to a single motor because I require a higher voltage. I notice the motor is not running quite as smooth, which is ok. I am just curious if there is any other risk when doing this?
You won’t get higher voltage from using the outputs in parallel. You’ll get (approximately) double the current, and if you control the inputs appropriately, you should not be able to see any difference in smoothness, at least not because of the hardware. If your software is making abrupt changes to the speed, you will see that in the motor more when the drivers provide the current for the motor to actually do what the software is telling them to. However, you should make sure that you are not driving the inputs in a way that makes the two H-bridges work against each other (typically, you would just hard-wire the corresponding inputs together so that they always have the same value).