Alright kids, it's time to learn about
faces!
See this rectangular prism (2x4 brick)?

It has six faces. Blockland makes it so you can see each of these faces. What if we add a 2x2 brick to the edge of it, how many faces are there now?

Six! The two faces that touch each other are not rendered since no one will see them.

If you were to set your camera inside a brick you wont see these faces. Why? they don't exist!
Let's say you made a tree out of twenty bricks, and had those bricks turned into one brick that looked exactly the same. That one brick would lag just as much as the twenty. Because in the end they still have the same number of faces.
These are problems with your request Neventii:
- Most servers only reach one fifth of the brick limit. Having multiple bricks as one serves no function do to this.
- A converted brick would act the same way as all the bricks it was originally made out of.
As long as there is no faces showing within what you build it will act as one brick. If you want to be able to move what you build around like one brick I suggest getting the
Duplicator. Go to page 28 of the topic and see how it works for painting the Duplication as well!
As Zeblote and The Resonate! have stated this request serves no purpose. Truthfully it would be worse then having multiple bricks because of how bricks work code wise.