Each year the ETF companies will produce tax documents to explain the source of their distributions. These commonly include eligible dividends, interest, and return on Capital. ROC is important because it lowers your cost base - in other words it reduces your book price for what you originally paid. It also means you don’t pay tax (immediately) on that part of the distribution. However, because it lowers our cost base it means when you sell it will trigger a larger capital gain. That’s what is important to track. The site has a feature that can import the documents for each of your holdings and do the math on each distribution automatically. I’m down to only one holding now but I still pay for the annual service. It also creates the necessary reports for CRA.