Most unlockables, modules and engineering upgrades that require something other than just credits, require materials. The good thing about materials is that they are essentially stored in a kind of "hammer space" that's completely independent of your ship, they don't require anything special in your ship to store them, and you can't lose them. This is very convenient when you are mining for a long list of materials that you need for some module or upgrade.
There's one exception, though (or at least the most notable exception): Many anti-thargoid unlockables require meta-alloys. The problem with metal-alloys is that they are commodities, not materials, which means they require cargo space in your ship and can't be stored anywhere else. This is inconvenient if you are kind of "mining on the side" while doing other stuff, changing ships, doing cargo transport missions (such as community goals) and so on. There's nowhere to store the meta-alloys until you need them! You just have to be constantly dragging them along in your cargo bay until you have a use of them. You can't even change to a ship that doesn't have enough cargo space for them, possibly locking you out of some of your ships (you can't even add cargo modules to such a ship because you can't switch to it!) And if you get destroyed, you lose the precious meta-alloys (something that's more likely due to the fact that Thargoids have a thing for them).
We already have free storage at space docks for modules that we don't need. It makes no sense to not have storage space for commodities as well. I would be willing to even pay some moderate rent for storage space if I ever need it. (Commodities could even use the same mechanic as modules in that you could have them transported from another space dock to your current one, at a fee, just like with modules.)
The advantages should be obvious: They don't take up cargo space in your ship, and you don't lose them if you get destroyed, and it allows for longer-term gathering of commodities for modules and upgrades that need them. If it costs some moderate weekly rent, that would be mighty fine. It would only make sense even in-universe.
There's one exception, though (or at least the most notable exception): Many anti-thargoid unlockables require meta-alloys. The problem with metal-alloys is that they are commodities, not materials, which means they require cargo space in your ship and can't be stored anywhere else. This is inconvenient if you are kind of "mining on the side" while doing other stuff, changing ships, doing cargo transport missions (such as community goals) and so on. There's nowhere to store the meta-alloys until you need them! You just have to be constantly dragging them along in your cargo bay until you have a use of them. You can't even change to a ship that doesn't have enough cargo space for them, possibly locking you out of some of your ships (you can't even add cargo modules to such a ship because you can't switch to it!) And if you get destroyed, you lose the precious meta-alloys (something that's more likely due to the fact that Thargoids have a thing for them).
We already have free storage at space docks for modules that we don't need. It makes no sense to not have storage space for commodities as well. I would be willing to even pay some moderate rent for storage space if I ever need it. (Commodities could even use the same mechanic as modules in that you could have them transported from another space dock to your current one, at a fee, just like with modules.)
The advantages should be obvious: They don't take up cargo space in your ship, and you don't lose them if you get destroyed, and it allows for longer-term gathering of commodities for modules and upgrades that need them. If it costs some moderate weekly rent, that would be mighty fine. It would only make sense even in-universe.