I bought AP 1.7 today and in setting it up, in Prefs I don't find a setting for a Scratch Disk. PhotoShop has used one for years for better performance so I would think AP would follow that method also. Please add it in the coming updates.
I second this. Usually, software needing to create big temporary files and taking care of the user's system disk (especially when it's an SSD) allow to specify a folder located on another partition. AF Photo is a good software but things that seem obvious for other similar software and that are really simple to implement (like a workspace manager and a user defined scratch folder) are merely ignored. This is strange.
It seems that AF Photo creates its scratch files in the folder pointed to by the TMP or TEMP user environment variable. I always set these variables to a folder located outside of the system disk.