You seem to be referring to the selection of candidates of files to transfer (along several possible criteria like modification time, file size or file contents using checksumming) [2]
Rsync is great. However for huge filesystems (many files and directories) with relatively less change, you'll need to think about "assisting" it somewhat (by feeding it its candidates obtained in a more efficient way, using --files-from=). For example: in a renderfarm system you would have additions of files, not really updates. Keep a list of frames that have finished rendering (in a cinematic film production this could be eg. 10h/frame), and use it to feed rsync. Otherwise you'll be spending hours for rsync to build its index (both sides) over huge filesystems, instead of transferring relatively few big and new files.
In workloads where you have many sync candidates (files) that have a majority of differing chunks, it might be worth rather disabling the delta-transfer algorithm (--whole-file) and saving on the tradeoffs.
[0] https://www.andrew.cmu.edu/course/15-749/READINGS/required/c...
[1] https://en.wikipedia.org/wiki/Rsync#Determining_which_parts_...
[2] https://en.wikipedia.org/wiki/Rsync#Determining_which_files_...
I would say most interesting texts (articles, books, school, ...) should leave stuff up to the reader's mind to figure out. That's how someone really learns. Versus pre-baked stuff like television etc.
If something does not resonate at first that's pretty normal. You could still take it apart and start investigating words or concepts that ring no bell, for example: waves, interference, demoscene, owls, Feynman.
Enjoy! ;)