Are you talking about mats, like Iron vs. Rubedite? Or are you talking about gear levels, like 50 vs CP 160?

As for mats, the only way you can craft various levels from Iron up to Rubedite (as an example) is to put skill points in the crafting skill as its levelled. You can be a CP 2000 and still only be able to craft Iron gear if you do not put skill points into Blacksmithing. Crafting levels progress only when you level them, independent of your overall character's level.

As for gear, its when your character reaches that level. So once you hit Level 50 that character will jump to the level of your highest character and be able to wear CP 160+ level gear, if that is your highest character's level.

Last, if you are planning on making alternates, you will want to keep lower level mats to craft gear for them.

If you do crafting writs, you will need each "tier" of materials as you level up your crafter's skills to make the required items like Galatite Armor, etc.

That's about the only time you'll need those materials, unless you frequently make gear for other people who are leveling for the first time.

And with most of the crafting disciplines, you can brute force your way past those levels quickly by deconstructing a bunch of inspiration gear if you don't want to do writs at that level.

@Bitter_Apple21 one thing you might consider is that your characters that do no have the skill points in those crafting skills, blacksmithing, woodworking, clothing, will have a lower chance of obtaining the raw materials. For example, your crafter will be able to go out in overland and the nodes will all be at the highest level. But if you take out your alternate who has no skill points in those skills, you will see a mix of highest level nodes and lowest level nodes.

I agree that there is no real reason to have two or more crafters, but I think it is useful to have the skill lines maxed out on all characters, along with unlocking all the traits on all characters (except nirnhoned). There are more than enough skill points to go around. Its also infinitely more convenient to be able to improve gear on any character than to have to put it in a bank, switch toons, improve it, put it back, etc. Same goes for reconstructing.

You get mats at your crafting level about half the time and at your character level the other half of the time. Continuing with your tailoring example, my CP1860 crafter gets ancestor silk half the time and ancestor silk the other half of the time as well. My CP1860 non crafter (without points in tailoring) gets jute half the time and ancestor silk the other half of the time. That said, all my characters have 'support' skills in crafting to better see mats, improve their chances of refining for improvement mats, making potions last longer, making food last longer. I just don't sink points into the ability to craft better items on newer characters since I already have two 9 trait maxed crafters for that.

@Bitter_Apple21 Its what @AcadianPaladin and @Nestor said, that you have the same chance at the node appearing, but it will be a split between it being the top level mat (rubedite, ancestor silk, etc) and the level your skill is currently at, which would be the lowest (iron, jute, etc). There will not be less nodes. I have friends who intentionally keep some characters at that level because they craft gear for others to make gold so they need low level mats. Since a lot of that is low level training gear, they want a healthy supply of low level mats similar to their supply of top level mats.

And to join in what @Nestor said about alchemy and provisioning, I also have those maxed on my characters (except for gold level provisioning). The passives are the primary reason, but also the convenience in crafting when I need it.