Ka,
If you are not vigorous with agitation, you may start to experience uneven development and loss of contrast. Maybe even bromide drag on the negative. This is not good. In my estimation more damage can be done to the negative with too LITTLE agitation than with too MUCH agitation. When I process roll film in cans, I quickly upend the cannister several times in the first minute and then rap the tank on the sink and then don't touch it until the next time and then I repeat the process. I usually agitate on the minute and only on the minute. Try it you will like it.

lee\c