The LAYERSTATESAVE command was added to AutoCAD 2010 with little mention – it's not even covered in the documentation – but it's useful for quickly saving a new layer state or replacing an existing layer state.
It provides a minimalist interface that only allows you to provide a layer state name and description. That's it. This is useful for those times when you're right in the middle of something and decide you want a snapshot of your layers as they are at that moment.
It's quicker than using the Layer State Manager dialog or the –LAYER command because it requires fewer keystrokes and no mouse clicks. If you assign it an alias, such as LSS, its even less keystrokes. Type LSS, type the name, and hit Enter. If you enter an existing layer state name it will ask if you want to replace it. Hit Enter one more time and it will overwrite the existing layer state with the new snapshot.
This dialog is also available in the Layer Walk feature. If you're using Layer Walk to inspect a bunch of layers and decide you want to save a current snapshot of the layers to a layer state, you can click the "Save Layer State…" option in the right-click context menu and get this same interface.
Sometimes people ask about all those options in the Layer State Manager dialog that don't appear in the LAYERSTATESAVE dialog. Don't they need to set those options to choose what layer properties get saved in the layer state? Actually, no.
Those options only determine which layer properties are restored when you restore a layer state. Every time a layer state is saved, AutoCAD automatically saves all the properties of each layer. This avoids a situation where you saved a layer state without saving the Lineweight property only to later realize you wanted to restore that property.