If you use Apple mobile devices, you may have recently encountered a display such as the one that appears above. The new operating system for phones and tablets from Apple now blocks what are called third-party cookies by default. You can change this default if you want.
A third party in comparison to a first-party cookie is using information you have stored from a website you are not currently visiting. This is how you can see advertisements for cars on Twitter when you were searching for cars using Google. A first-party cookie shows you ads based on the website that is currently active.
I am against blocking cookies because this is the way you compensate the content creators and service providers for using their resources. I am not against blocking third-party cookies because the ads you see are not directly related to the site you are visiting or the service you are using. This seems fair.