Topping cannabis is a great way to manage your canopy and is only done in the vegetative state. Some people have height restrictions and topping can help to keep your plants short, stout, and bushy.
Topping is a simple and effective way to increase yields by maximizing canopy space and allows more bud sites to get even distribution of the light. This is important because it results in bigger dense buds, better yields and improved utilization of the production space.
In order to top cannabis, you will need a pair of scissors with a fine point to get a precise cut and alcohol to sterilize the scissors is highly recommended to avoid the risk of passing on any pathogens when making a cut.
(If you are topping multiple cultivars it would be good practice to clean your scissors each time you start a new strain.)
Another method would be to scoop the node out with your fingers if you are not taking much off the top.
(If you are cutting a couple inches or more off it would be better to use scissors to minimize the damage.)
Naturally, cannabis grows with apical dominance similar to a pine tree. Topping the main shoot by removing the top node will cause the next two nodes to grow into two branches and promote lateral growth.
Generally, topping will slow down the shoot or shoots topped allowing for the lower branches to catch up with the rest of the canopy helping it to even out. This can enhance the overall structure of the plant depending on the cultivar. Some cultivars respond better than others to this technique.
Other perks of topping is it allows you to take some healthy tops for clones to preserve and further production with the same genetics, and you can snag some healthy tops for cuts to further production and preserve genetics.