Can you use the dendrogram to make meaningful clusters? (By looking at which elements leave and join at what height)

Yes. It is a great tool. You can look at what stage an element is joining a cluster and hence see how similar or dissimilar it is to the rest of the cluster. If it joins at the higher height, it is quite different from the rest of the group. You can also see which elements are joining which cluster at what stage and can thus use business understanding to cut the dendrogram more accurately.