ETFs publish the list of their holdings every single day. It makes it extremely easy for you to keep track of your investments. Mutual funds, on the other hand, tend to publish the list of their holdings infrequently. There are some actively managed funds which are known to publish their holdings every two or three months.
The problem with such a long gap is that any changes made to the holdings remain unknown to you until the report is published. With ETFs, you know what you are invested in at any given point of time.