I shoot with Sony A7r4 and I use sections from multiple photos to stitch together a perfect shot. I work with 16 bit layers only and typically my PSD files reach the size of 10GB+. My shots have appeared on billboards so I will need to retain every bit of quality possible.
Once a file becomes too big, saving takes a long time so my strategy so far is to break a workflow into multiple files.
For example: Let say I have a photo (let's call it base) that involves 5 operations A, B, C, D, E
v1.psd will be the base image + operation A.
v2.psd will be the output from performing merged visible in v1.psd + operation B
v3.psd will be the output from performing merged visible in v2.psd + operation C
v4.psd will be the output from performing merged visible in v3.psd + operation D
v5.psd will be the output from performing merged visible in v4.psd + operation E
The merged visible of v5.psd will become the final output.
The only issue with this is that if I make a change in v1.psd, I will have to propagate the changes by merging visible in v1, copying that to v2, merging visible in v2, copying that in v3 etc etc.
It would save me a lot of time if it is possible to create a live layer in PS based on another PSD file. What this means is that if the imported file is modified, the corresponding layer will automatically update. If this is possible, I wouldn't have to merge visible multiple times for every file downstream from the change I made.
