I've seen this in a few other games, namely Minecraft and Robocraft. While in creative mode, clicking on a block with the middle mouse button will modify your current inventory slot as though you went into the inventory screen and selected that target block.
In the case of Starmade, an example would be middle clicking on a Purple Advanced Armor Wedge would replace your currently selected inventory slot with the Purple Advanced Armor Multi-block with the wedge option currently selected.
The obvious benefit is that creative builders can spend less time digging through the inventory when they need to modify part of a ship they haven't been working on lately.
In the case of Starmade, an example would be middle clicking on a Purple Advanced Armor Wedge would replace your currently selected inventory slot with the Purple Advanced Armor Multi-block with the wedge option currently selected.
The obvious benefit is that creative builders can spend less time digging through the inventory when they need to modify part of a ship they haven't been working on lately.