No. The purpose of the form is to allow people to make decisions for you in the future, if you can no longer make them yourself. It does not mean that from the moment you complete the forms your attorney takes over making decisions for you.
If you make a health and welfare LPA, your attorney cannot make decisions unless there comes a point where you cannot make them yourself.
This is different for the property and affairs LPA, which allows you to say whether you want your attorney to be able to act while you still have capacity. If you do, they wouldn’t be taking over from you, as you will also be able to act. It means that your attorney will be able to help you manage your finances and help you make your own decisions.