That sure isn't the only time I trim my plants, especially if they're indoors. If you've got to control size, you've just got to, period.
If you want to control the size of the plant you got better ways of doin it, scrog the plants and if they get to close to the light just tie them down, but never take away the food supply.
And if you want to control the size otherwise you just have to get a bigger place to grow or put them in flow stage earlier.
http://www.youtube.com/watch?v=xYq7CuVpAeo