Browsing in PhotoLibrary (and not click one-by-one) itself (for me) is okay (on old not so fast SATA SSD ). With few 1000’s photos IF the folder was never opened than takes a time, but runs well (as i test, usually i have like 20-50-100, 500 is rare)
Just browsing (and not click one-by-one) + edit applied, is can be fine - once the folder indexed, you already goes thru the photos, etc.
A few months (?) ago i check in details what’s happen when folder open, etc. . Some details in here about tons of folders, etc, and quite details on what’s happening during folder opening here, may others about in that threads.
TLDR: i think PL is fast on folder opening.
“images back-and-forth”
Yes.
Somewhere i write in some details what happen like A ->B → A “back and forth case” -in editing - but i not find it yet.
I the nutshell as i remember: Click on A → PL read up first the already generated ‘cache’ folder ‘Preview’ jpg and display it - its not a full 1:1 jpg, some like 1000 pixel wide (that’s the reason you see immediately something) - i think all Phot app do more-or less the same way (like C1 also use some mid resolution, mid quality jpg). And its start to create the ‘full preview in progress’. If no editing, or just some base → its fast. If AI masks → it’s takes time → But time as the hardware as-it-is! Dont forget, its create (to memory) multiple versions: without geometry, w/ geometry, w/ editing w/local adjustments. And its create 1:1 full quality for editing. Now click to other one (A ->B). First its re-create the ‘Cache’ folder preview and thumbnail jpg. I think the main reason for that at this point the ‘whole 1:1 edit quality’ is in the memory , and that’s the best time to update this jpg’s. And do with B the previous.
Some ‘culling’ mode may can help on that (when no ‘full preview in progress’ happen, just use the ‘cache’ preview jpg). However, if you do some ‘multi edit’ or manually apply preset for a lot of photos, or zoom to 1:1, etc → its not helps.
PL creates a new preview with every image navigation.
See previously.
Note: A → B → C case - if you wait until the ‘generating’ small circle finished, than may can save some time for ‘full preview in progress’. A ->B wait until A small circle finish, and than go to B → C.
May ‘if no change’ than not re-generate ‘cahce’ folder preview+thumbnail. However the ‘nothing change’ can be true if really nothing change → But like change Exposure with +1 and after change Exposure with -1 also give a ‘nothing change’, can be an issue, etc.