You can use any folder you like - the public documents folder is just the default. If you are planning to share content I would advise creating a folder only for your content, or even one folder per project if you work on multiple projects at once, and select that as a DAZ Studio Content Directory (most easily done by right-clicking on DAZ Studio Formats in the Content Library panbe). Place your textures in that folder, and when you save assets set that as the base path or when you save presets save them to there - that way you should get a folder that contains all and only the files for your item, ready to have a readme added and to be zipped up.