When resetting your Chrome settings to default, you restore your browser settings. This means the ‘New tab’ page, search engines and pinned tabs will be reset. All extensions will be switched off and all temporary date (such as cookies) will be erased. Your bookmarks, browser history and saved passwords won’t be cleared.
When you PowerWash your Chromebook, you reset your Chromebook to factory settings. This means all data of your hard drive will be erased, also the files in the “downloads” folder and all accounts on your Chromebook. After a PowerWash, all setting have to be re-installed, also the owner account.