Many people are not aware of the difference between the two. But, in general, a lawn sweeper is more efficient for large grassy yards and baggers are better for small and dense areas.
One of the main differences between a lawn sweeper and a bagger is that a sweeper removes debris before it gets to your yard whereas on a bagger you have to pick up everything. Another big difference is price - an average lawn sweeper will cost about $50 whereas an average bagger costs about $25.