The ability to terraform a planet would move humanity a step closer to becoming a Class 1 civilization.
Popular physicist Michiu Kaku posits that there are 4 potential levels of civilization in the universe.
Class 1 Civilization: Edit
Able to exert effective control over planetary bodies
A Class 1 Civilization can effectively harness and control weather, atmospheric makeup, volcanos, plate tectonics, and other planetary forces.
A class 1 Civilization can not only control their home planet, but can effectively control other planets to the extent such an effort is practical, such as terraforming nearby planets for colonization or other purposes.
Class 2 Civilization: Edit
Able to exert effective control over star systems
A class 2 Civilization can effectively control entire star systems, including the star itself. Custom designing planets and their order in a star system are within the abilities of such a civilization. Additionally, the star itself is effectively harnessed and controlled, to the extent that a star on the brink of supernova may be stabilized, its characteristics changed, sunspots and flares directed or abated at will. For this civilization, creating or destroying a star is a merely construction project (albeit a big construction project that would tax a Class 2 civilization's resources), and the star is a likely source of near limitless power for them.
Class 3 Civilization: Edit
Able to exert effective control over galaxies
A Class 3 Civilization can effectively control entire galaxies. They are able to harness and control black holes, and alter or cause spiraling in a galaxy, as well as control the placement of constituent stars within the galaxy.
Class 4 Civilization: Edit
Able to exert effective control over the known universe
A Class 4 civilization has effectively reached godhood, as it has an effective control over the laws of physics itself, on a micro and the most macro levels. From creating a big ban to slowing and reversing expansion, a Class 4 civilization is nearly all-powerful, and can literally create or alter space, time, and any other aspect of existence. The ramifications of such a civilization are mind-boggling, and as nearly impossible to comprehend as the concept of infinity.
I suppose one might argue that there could be a class 5 civilization, which could exert control over the multiverse. We'll wait until the multiverse is a bit more scientifically solid to go there.
Kaku takes delight in reminding us that on this scale, we are a Class Zero Civilization - that is, we don't rate at all. We aren't even on the scale yet, so pathetic are our skills and grasp of practical physics.