Symbols is one way to resuse your work. To have one place to go to for updating the same asset is onderful, and you can also use Libraries for the same purpose. But the problem is that they offer different options and limitations.
Symbols can be "global" in the sense that they can be resued and updated for multiple instances within a file, but it's not fully global so it can update the instances over multiple files. For this I can use Libraries. But, there are limitations...
First, I can't find a way to set colors in Libraries with a Opacity setting. For the same reason I put the color there in the first place, I want to be able to control the opacity in one place, not for each object that using the asset. Ok, then I try to put the Library asset into a Symbol so I can control this, but this is not allowed. 😞 Is there a way to get around this?
Next, I have Symbols that are nested with other symbols so I can control multiple levels of options, turning on and off different "branches" of a tree. This allows me to keep the numbers of Symbols down, and provide opportunity to test different alternatives. I've mentioned Opacity that is working as I want to when using Symbols, but there is another function I would like to see that don't work in any of the two methods - I want to be able to control the line weight so I can change this setting and it will update all the lines with this new value. Is there a way to do this? Perhaps character styles - but I thought that was only for text?