Edit List View is a function provided by Odoo. Even though it'll not create any system errors while used correctly, It's better to create a custom module for any customization done. In that way, you'll have proper record of all the updates done to Odoo.
Some points to note while using Edit List View:
- Changes made will be lost once you upgrade related module [for example a list view created from purchase module is updated from UI. when you upgrade purchase module, the list view will be loaded from code and your updates will be lost. This might cause system error, based on your code]
- A new field cannot be created from this view. Only already created fields can be added to the current list view.