Every single time I've used the InputIterator constructors of various containers (e.g. vector or set), it's been to convert an existing container from one type to another (e.g. set to a vector). As such my code could've been simpler and more concise if the constructors simply took a container as an argument and did the begin/end internally.
Any reasons to not have such constructors? These are trivial to write and I'm happy to provide the code, but perhaps I'm missing something.