Practical usage of wildcard generics in Java

I recently had an exam on Java, and there was a wide section about wildcard generics in Java. However, there is very little said about their usage in practice. When should we use them? Let's see a typical usage: ``` void check(Collection<? extends Animal> list) { // Do something } ``` What the documentation says, that this collection does not allow to add any elements to the list. So basically wildcards can be used for making collections read-only. Is that their only usage? Is there any practical need for that? For the last four years I took part in a lot of programming projects in Java, but I haven't seen any project that would use extensively such a feature as wildcard. So, from the practical point of view, are there any situations when wildcard generics are unavoidable and necessary?