I have found that Carrara’s UV editing has a steep learning curve, but it has been worth it to learn and use. I’m very much a novice, but as an example I have fixed UV mapping on purchased models where there was significant stretching (not noticeable depending on how the model was positioned, but very annoying for how I was using it). And of course if you are doing your own models you’ll want to create UV maps.
I highly recommend reading up on UV mapping to get an idea of what you are trying to do. Carrara can create a UV map based on box, sphere, etc., but if you spend the time you can use the seam tool to identify where it will be “cut”. Then use unfold to obtain the results. When I made RPG dice models (polyhedrons) this was very straightforward. Conceptually it works by putting the die on a surface that takes an imprint of the face touching it, then tip it over an edge so that a different face is touching and repeat until every face has touched the surface exactly once. What you then have is a “path”: the edges of this path are where the seams are.
One thing to note is don’t bother trying to clean up the unfolded uv map until you have gotten every shading domain to unfold satisfactorily. Once the unfolding is good then you can scale the different parts, but each time you unfold will re-unfold every domain.
To check for stretching and alignment use a grid texture map—it is easy to make one in photoshop, the gimp, etc. Apply that, set the repeat as desired and carefully inspect.
Note: I’ve not used any other tool to do UV mapping so I have no basis for comparing Carrara’s UV editing to others