Sculpting is a great way to add a lot of high resolution detail to your models in a very intuitive way. And for most applications, you can sculpt your geometry without worrying about having a UV layout. A UV layout defines how a 2D image or texture map is wrapped onto a 3D surface. UVs usually only become necessary when you begin painting textures or you want to bake out normal maps. (In ZBrush or by using PTEX you can paint models without having UVs at all.)
It's not always a fun process but is often a necessary one. Although there are times when we can forgo the UV process, (or at least put it off until later!) sometimes a clean UV layout during the sculpting process can allow you to quickly create effects or details in ways that would otherwise be very difficult.
Sculpt with alphas or textures
In some cases, using an existing map to add sculpted detail can save you a lot of time. For instance, you may want to sculpt the tread of a tire by applying a tire tread texture and raising the detail appropriately. The layout itself will differ based on the type of model, but it should be created with the texture map in mind. Think about how you want the detail wrapped around the model. So in the case of the tire, you'll want the UVs to be laid out straight to match the texture map. Then you can apply the map as a mask or displacement. This detail can be "baked" into the sculpt so that it's not dependent on the map any longer and you can continue sculpting.
Creating clean patterns
If you're creating cloth, upholstery, or maybe hard surface pieces that need to have a clean, repeating pattern across the surface, UVs can be a great way to achieve the right look. You can manually paint the detail using stamps or stencils, but adding that detail in this way may result in blurry edges where the stamp or stencil borders are visible, especially on large or complex surfaces. By using your UVs and adding the pattern as a texture or displacement, you can create an even, seamless pattern that covers the entire surface in exactly the way you intended.
Generating procedural detail
In ZBrush you have the ability to add patterns using the NoiseMaker plugin. (Tool>Surface>Noise>NoiseMaker) There are tons of patterns to choose from and they will work if your object doesn't have UVs. However, they'll look a lot better from all angles and cover the surface as intended if you create a UV layout for your object.
Depending on the sculpting application you're using, you may not have a lot of control over the exact UV layout of your objects. In ZBrush, you can try using a Planar, Cylindrical, or Spherical projection from the UV Map sub-palette. For more complex shapes, the UV Master plugin will quickly unwrap your model for you. Mudbox will create some simple UVs, but this layout will usually not be too useful in these instances. When you want ultimate control of the UVs, which is likely what you'll need to get the results you want, you can use GoZ or "Send To" to export your object and edit your UVs in another application. You can create a UV layout specifically crafted to use a particular map. Don't forget to update the sculpted object with the new layout.
You're used to using UVs for painting textures or baking maps, but try applying some sculpted detail using maps and a good UV layout and you'll save time and get great results!