Low-density vs high-density growing

Right now I have two 3*3-feet tents with Wilma 4's inside. What I intend to do is to upgrade to a single 5*5-feet tent and have a Wilma 20 inside that. This means that the area for each plant will be roughly halved.
What does this mean in practice? Can I, for example, still use the lower buds?

You can use whatever you want? There are way to many variables, i.e, what are your growing methods? What medium? Do you have a veg chamber? You should be able to answer your own question after answering all of the above.