It helps to a certain extent, all depending on your light, space, and plant amounts are. Your plants will only grow as well as their worst limiting factor, in most cases the light. So if you have a bunch of plants and are trying for a sea of green than you want to switch to flowering as soon as you can to get a bunch of single colas, however if you can only have a few plants and have the time to top your plants and really grow them out then your yields will certainly be improved. I had a friend who vegged for about 8 months or so and his mama was about 4-5 ft in diameter and over 4 ft tall, it made for one hell of a trimming day!