i was reading a book yesterday on how to make your own foundation, my question is what would happen if you left the impressions out of the sheet. Would the bees still build good comb? or would it be bad comb.
That depends on what you think is "good comb" and "bad comb". For a century or more people have been trying to force the bees to not build as much drone comb and then to build bigger and more uniform cells.
Since the latest research says the bees will raise the same number of drones regardless of how many drone cells there are (which was actually observed by Huber in the late 1700's) I don't see this as a problem.
The other issue is small cell brood cells. Bees will actually build a wide variety of cell sized based on their intended use for the cells. Natural sized bees will build cells as small as 4.6 to 4.9mm for brood rearing and on the outskirts of the central brood cells they will build some as big as 5.1mm for brood also. These transition into drone brood at about 5.9 to 6.6mm and honey storage which may be as small as 5.9 and as large as 6.6mm. They will store honey in anything that is available of any size that happens to be where they want to put honey, but will build it larger if storage is their main intent.
The point of all this is that you will have a beehive organized as the bees wish it if you let them (with blank foundation or blank starter strips). You will have much more UNIFORM comb if you use embossed foundation.
The "interchanability of combs" issue is that if you put oversized comb (from honey storage) in the brood nest the bees will raise larger bees or maybe drones in it.
If you use blank sheets the combs are not as interchangable.
All of that said, My favorite is to make blank sheets, cut them into strips and just use umembossed starter strips.
I have not used full blank sheets but others have said they work ok.
When doing this, I try to keep the brood comb in the brood area and the honey comb in the honey areas and not mix them up.