What Happens When You Delete Cookies?by Aaron Parson
Effects on Accounts
Clearing your cookies will log you out of every website you've logged into online, even those where you checked "remember me" or "stay logged in." Once you log in to a site again, the website will recreate the deleted cookie. While generally a negative effect of deleting cookies, deleting and recreating login cookies can also fix account problems on some sites, such as being unable to stay logged in to an account.
Effects on Settings
When logged into an account on a website, any settings you change are generally saved to your account data online. If you change a website's settings -- for example, the search options on Google -- while not logged into an account, these changes are often saved as cookies instead. Deleting your cookies will remove all these settings, bringing your site experience back to the default, so you will need to re-customize your settings if desired.
Effects on Tracking
Some websites create third-party cookies from advertising and marketing networks such as Google's DoubleClick. These cookies can report back on your browsing behavior across many websites. The companies use this information to customize the ads you see online and compile statistics. Deleting cookies will interrupt this process, separating your prior online activity from your future activity in the trackers' data. The only noticeable effect this will have for most users is a change in the types of ads that appear on websites. Google also uses this data to customize the results you see on its search engine, so deleting cookies will revert Google to showing un-customized results.
Deleting versus Blocking
Since most websites recreate deleted cookies quickly, some users opt to completely block cookies instead. While this will effectively prevent tracking, it has a number of major downsides. While blocking cookies, you'll need to log in to a site every time you use it. Some sites will fail to keep you logged in even from one page on the site to the next. Other websites will display errors or not function correctly with cookies blocked. As a middle ground, you can choose to block cookies by default, but allow them for certain websites.
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