I've been in sprints where there are lots of little things to be done, as well as sprints where there's just one thing that has to happen. My experience is having one big target is much better than lots of little targets.
The reason, I think, is that one big target lacks the context switching that going from target to target. It allows all people to focus on one problem and gradually work to that.
A big target is not an ill-defined target. The same rules apply as apply in all scrum - it should be coherent enough that it can be worked on. Anything less and a big target has a chance of failure.
A big target should still be broken down to small targets. But the package of targets together provides a context to the work. A package of disparate targets has their own context, with the developers needing to adopt that mindset to begin work. Smaller tasks for a greater whole do not have that problem.