I don't know how it is for large businesses, but if you're a small business, and you put your own business name as a search keyword for your ad buys, fully half or more of your ad spend will be your existing customers looking for your website, phone number or address. If you stop spending on it, they will still find you, but a competitor will probably show up above you. I am not sure this matters.

Google has been sued for displaying ads on trademarked keywords though.