A long time ago in Final Fantasy XI, People complained that the shield slot looked boring being empty if you were weilding a two handed weapon. In response, we got these things called Grips.
Basically the lore is, they were custom leather or other fabric strips that wrapped around the handle of your two handed weapon and gave you a bonus.
More Strength, More Critical Hit, More Intelligence etc. These were awesome replacements when your character can't wear a Shield.
So why wasn't this extremely original option (I hadn't seen it in any MMO or Single Player game before or since.) replicated over to FFXIV? Come on SE. Give us our Grips!
The difference is you are not adding a second slot like you would for the second earring, You are using an already available slot (Shield) to allow non-shield available classes to use an empty slot.