How detailed can 3D clothing samples be? The answer is, however detailed needed to meet the goal. If you need every stitch shown, it can be shown. 3D samples can include hardware; like buttons, rivets, and zippers. Fabric textures can be shown such as the rib collar in the below slideshow.
Yes, it takes time and effort to add details, so if you are using 3D as a collaboration tool to explore style options during development, you may not need or want all the details. For instance if you are working with the designer to get an idea of the drape of the fabric, the fit of an armhole, or the depth of a neckline, you may not want to spend time and effort adding details. You can wait and add the details once the fit and styling are firm or go directly to physical samples.
If you are trying to convey the garment construction to a factory, you will want to add every stitch detail. Or if you are using 3D in place of actual samples for a client presentation, all the details are needed.
3D samples can also offer an opportunity to review the proportions of details such as button, buckle, or ring sizes. What length should the placket or vent be? How deep should you make a cuff or hem? Bottom line is, 3D offers many opportunities to make decisions before producing physical samples.