The way I see it is that throws are harder to execute properly, consistently, against a variety of different body masses.
I would say that locks are more subtle when it comes to getting one's energy to enter the center of uke - which is what is necessary for throws. Things like momentum/inertia, etc., allow for a lot more leeway in getting someone's balance. Either way, for me, one should have throws in one's locks and locks in one's throws. Here's a simple throw located in the middle of a nikkyo variation - it's near the end of the video:
Here's a simply throw located at the beginning of a nikyo variation: