For me personally it is a very useful tool for setting my investments, especially for a long-term plan. It is a very versatile feature and having automated functionalities is simplifying the portfolio management (especially rebalancing). It is something that I was thinking about since I started my financial journey.
You should check exactly how this feature can fit your goal and strategy (if you invest in just 1 share/ETF it will not be very helpful). But to get more in-depth information about this tool you can read this initial description or even this initial pie idea thread. Also you can check the discussion of other users regarding their use of AutoInvest.