When converting photos from RAW to TIFF then Adobe Bridge is putting extra thumbnail to image files called "Photoshop Thumbnail". The problem is that some other photo editors (like GIMP) can't handle correctly that thumbnail.
Currenlty I must every time remove the Photoshop Thumbnail with Exiftool (-photoshopthumbnail=) but sometimes I forget to do so...
In what way does the "Photoshop Thumbnail" affect other photo editors like Gimp?
Because "Photoshop Thumbnail" is not necessary metadata. GIMP (and maybe other photo editors) does not update that [photoshop-] thumbnail after editing and it may be privacy risk.
I don't even understad which is purpose of the "Photoshop Thumbnail"? Currently it seems that its only "bad metadata".
Its not "bad metadata", its the thumbnail image for the file. Thumbnails are helpful when you are working with large files because a viewer can show that rather than having to parse the entire file just to show a preview.
Yes it is. "Photoshop Thumbnail" is pointless because image files also have another "official" exif thumbnail.
Thumbnails are optional. I don't know which formats have the thumb embedded, one of the Adobe developers would have to comment.