Watchlists are useful because you can change the items within the watchlist at any time, and any rule referencing that watchlist automatically uses those new items. Start modifying a small watchlist, and progressively add to it after you have a good understanding of the various configuration options.

For example, if you want to create multiple rules regarding the stock portfolio, you can create a watchlist containing all the stock symbols in the current portfolio. While creating rules, you can reference the watchlist instead of specifying each individual stock symbol in multiple rules. In the future, if your stock portfolio changes, you can change the watchlist instead of changing each rule.