See the following Apple articles:
About the 'Trust This Computer' alert on your iPhone, iPad, or iPod touch
About the 'Trust This Computer' alert on your iPhone, iPad, or iPod touch - Apple Support
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What the trust settings on your device mean
When you connect your iPhone, iPad, or iPod touch to a computer or other device for the first time, an alert asks whether you trust the computer:
- Trusted computers can sync with your device, create backups, and access your device's photos, videos, contacts, and other content. These computers remain trusted unless you change which computers you trust or erase your device.
- If you choose not to trust a computer, you block its access to content on your device. You'll see the trust alert every time that you connect your device to that computer.
Authorize or deauthorize your computer for iTunes Store purchases
Authorize or deauthorize your computer for iTunes Store purchases - Apple Support