I’m sure this has been done before, but here’s a simple file size comparison for using detail components vs. using detail groups. I took a simple 1x4 and made a detail group out of this using six lines and arrayed it 100 times in one direction and arrayed the array 100 times in the other direction. You can see images of it below. I then took the out-of-the-box Revit detail component of a 1x4 and inserted that into a new file starting from the same template and arrayed it the same way. I then saved the files as new files (to compress them) and checked the file sizes. I did the same thing for one instance for both the detail component and the detail group.

The results are telling - the single instance files are exactly the same size, but the file with 10,000 instances of the detail group is more than twice the size of the corresponding file using detail components. Now, I admit, 10,000 instances is a lot of instances so I did the math¹ and using the detail group ended up adding about 100 bytes per line. That could add up to something not too insignificant.