They create products with features like that because if one does it, they all have to do it because people comparison shop and a feature they don't have is a negative. Whether or not that feature is useful isn't as important to them as selling units.
Many receivers these days allow you to adjust the x-over frequency to better suit a specific speaker. YES, limiting the sound sent to a given set of speakers by using a higher x-over will give you more headroom on the receiver because you aren't driving the speakers as hard. In order to no have a gap in sound though, the sub has to pick up that work. Lower frequencies tend to take more power to reproduce, and the benefit of having the sub do it is that your sub has its own amp for the heavy lifting