Difficulty+ isn't for everyone.
Think that Starbound is too easy? Do you think that Mother Poptop poses zero threat. You can do the Erchius Mining Facility mission in your sleep with nothing but the broken broadsword? Have a bunch of mods that make Starbound too easy and want something to balance them out? Wonder when I will run out of questions and actually get on to what this collection does?

Difficulty+ takes the laziest and most mod compatable approach to making the game harder: by nerfing the player through boosting everything's damage and health (the player also gets a damage boost, just not health). That is all it does. You effectively have less health (about 2/3rds less).

The addons help compliment Difficulty+ by changing it further, but do not actually require Difficulty+. This means you can still have the changes caused by the addon without ever having Difficulty+ touching your game.