You've got just one inbox, but you need to sort your messages by source — shopping sites, newsletters, work accounts? The plus sign in a Gmail address solves this without ever needing to open an extra account.
You can add a plus sign followed by any word (a tag) right after your username, before @gmail.com. So if your email is john@gmail.com, you could use john+shopping@gmail.com or john+work@gmail.com, and every message still lands in the exact same main inbox.
Opening a new Gmail account for every purpose means managing multiple passwords, checking more than one inbox regularly, and risking forgetting about an entire abandoned account. A plus tag gives you the same organizational benefit without any of that added complexity — everything lands in the same place, and all you need is a simple filter to sort messages automatically.
From Gmail's settings, you can create a filter that searches for any message addressed to a specific tag (like "shopping+"), and assign it an automatic action — move the message to a separate folder, label it, or even skip the main inbox entirely if the tag is for something non-urgent.
Instead of typing out each address manually every time, the Gmail Plus Alias Generator gives you ready-made common tags (shopping, newsletters, work, banking, free trials) to pick with one click, or lets you type your own custom tag, with instant copy for every address you generate.
Yes, other major services like Outlook, Yahoo, and iCloud support the same general principle, though details can vary slightly between providers.
Yes, from Gmail settings you can create a filter that searches for the specific tag and applies an automatic action like moving the message to a folder.
Yes, some older sign-up forms treat the plus sign as an invalid character and reject registration, even though it's a standard, valid part of the spec.
No, only a single tag can follow the plus sign in each address, but you can create an unlimited number of different tags for different purposes.
The plus sign is a simple, standard solution for organizing your mail without extra complexity — one minute is enough to start using it on every new sign-up, saving yourself inbox clutter in the long run.