When it comes to public cloud, access control is very important part in it.
It is recommended to use roles for services then using crentials when using AWS lambda. Custom plocies are then very important and there mangement ver critical.
You should be in control of what roles has what kind of access.
This sctipt lists all your custom policies and actions assigned to it.
You can find script here.
Please note you will not get inline policies with this.