Address replacement is a security risk that can be caused by malware or virus during receiving or making payments.
It is possible to verify the authenticity of the address with the Show on Trezor feature to make your payment more secure and battle phishing and address-replacement attack vectors.
When copying the address created by Trezor Wallet and sending it to someone who wants to send you cryptocurrency funds (eg. copying to email), it is highly recommended to check the address with the one displayed on your Trezor device with Show on Trezor feature.
If you wish to make a payment to someone on the Internet, you need to know their address. Unlike Trezor, computers are not necessarily secure and it is possible that the bitcoin address displayed on your computer screen has been maliciously modified.
Therefore it is highly recommended to check the address shown on your Trezor device when confirming a transaction to the address you want to send the transaction to.
See also Making payments - Confirm on Trezor
See also this blog to learn more.