You've got several methods in controlling your plant height. Everything from supercropping (which involves snapping branches/stems) to trimming to tying down can be done, it's all dependent upon your purposes.

For example, I'd tie a plant down if I want it to spread out, and to help accomplish this I combine trimming the top off with a couple of days of growing to allow me to get side branches large enough to tie down and begin training. This does increase the density of the plant, however, so you want to make sure you have light penetration to get into the denser parts of the plant.

If you took a starting sprout and tied it down after 3 or 4 nodes without topping, you won't get so bushy.

Results and mileage will vary.