I ran a permission matrix report on a site collection. Holy ****! It returned 19,000 (with 3 zeros) items. Running the report took 20ish minutes. Then expanding took 20ish minutes. Then exporting it took 20ish minutes. In the end, it was a 330MB file.
It would be nice if it didn't take so long.
now.. i tried running a permissions matrix on all 1900 sites. it ran and completed. then when i tried expanding it, well, let's say 24GB of ram wasn't enough. It eventually caused the VM to crash.
So, maybe, just maybe if some optimization was accomplished, it would reduce the time on running, expanding and exporting permission matrixes.

thanks.