For folders that contain pictures, I usually set the icon size to maximum to see larger thumbnails. For document folders smaller icons and as default 128px size. Dolphin doesn't remember the icon sizes for individual folders despite the option being "Remember view settings for each folder individually"

Reproducible: Always

Steps to Reproduce:
1. Open Folder
2. Set icon size to maximum
3. Navigate to subfolder
4. Set icon size to minimum
5. Go back
Actual Results:  
After 3: Icon size in the subfolder is at maximum like in the start folder
After 5: Icon size is at minimum like in the subfolder although it should be maximum

Expected Results:  
After 3: Icon size is the default because it hasn't been set for that particular folder (or maybe inherit it when not set)
After 5: Icon size is maximum because the start folder has maximum set by the user