Address reuse is a security and privacy issue in the crypto space, affecting any blockchain project that uses addresses. You can read more about it here. In short, with a combination of address reuse and social engineering, a malicious party could identify you and how much cryptocurrency you hold.
When it comes to your Siacoin addresses, we try to avoid address reuse whenever possible. The Sia network is a blockchain project just like Bitcoin, and – in a worst-case scenario – your privacy could be compromised with address reuse. Sia-UI will create a new receiving address whenever you clickGenerate New Address. This is intentional.
Your old addresses still work! Every address generated by Sia will always link to your wallet. You can re-use previous addresses if your risk tolerance is higher than the risk created by doing it.
It can vary, and you should learn more about address reuse before making a decision. But most people seriously involved in the crypto space will tell you to err on the side of caution, and re-use addresses as little as possible.
To find a list of all addresses linked to your wallet, go to the Terminal tab and type:
wallet addresses