If you are going to be editing a texture file multiple times, or predictively, if someone else might be editing a provided texture file (which many do) saving as jpg is a compression format. Every time you resave the edited file it's recompressed. Or you can save with very high quality save settings in the jpg save dialogue but there will be compression nevertheless. All that compression over time results in original quality loss. It might be imperceptible or it might be very noticeable. Probably, most likely, a high quality save of a jpg after one edit will show no difference in quality. If you're someone who tweaks and changes a texture file many many times you'll probably be doing that in a layered psd file which will be uncompressed. Saving as png is useful for texture files that will be used in various other softwares besides Poser, it's an uncompressed file format that supports alpha channel (transparency and associated masks). You can also flatten png to background in an image editor and it will result in an image much like jpg but non lossy. This dumps the alpha channel. Downside is larger file size. I save everything as png (flattened or on a transparent layer depending on use) or psd. Most commonly texture files you'll find in products for Poser will be in jpg format to reduce file sizes. For posting gallery images or forum posts that are one time final images for that destination jpg is fine, because I'm nitpicky about compression I post as flattened png. Forum posts images also support transparency in png.