Weeeell. If you trim the other bud sites besides the top cola, the top cola will recieve more engergy to grow. I'm doing it on my runt plant. It's 18 days into flowering and now has a 2 and a half inch bud, bigger than the rest simply because i'm making it grow that way. By cutting off the side bud sites, it'll make the top cola grow strait up into a nice, huge bud. Makes harvesting and curing easier too, as well as a nicer looking bud. It's not recommended by many people i'd say, and i owuldn't do it to all my plants. But if you want to, and you do it right, nothing can happen to your plant but a bigger top bud. You'll still get the same ammount of bud though.
Also, if you want the bottom to get light as well as the top, you should look into LST, you can tie your plant down some and the light will get to the bottom bud sites as well as the top. Ooor you can pull back certain leaves and tie them there so that the light will raech to the bottom, or like slim said you can harvest the top and then harvest the bottom later on. Good luck with whatever path you choose my friend, take care!
~Burn one~
Dewayne