A deterministic generation function does one more very valuable thing from an auditability perspective that has nothing to do with recreating wallets. Supporting deterministic generation from a passphrase allows the average user to control for the possibility that the RNG in your generator isn't rigged or flawed in a non-obvious manner. If your RNG turns out to be flawed at any time down the road, it would turn into a huge liability for anyone who has ever used your generator. (Google "Debian OpenSSL key flaw" for an example of a past occurrence of this mess). On the other hand, if it produces the same deterministic wallet as any other program made for the same purpose, it can be conclusively deemed to operate as advertised.
The Wallet Details tab can now be used for the purpose of creating a deterministic wallet. You can use the tab to determine if you have a valid private key in one of various formats and what the bitcoin address is for that key.
It's also useful if you're in a highly adversarial environment and you believe a weakness in the PRNG could expose your private key. To protect against that you could copy the key you generate on the single wallet tab and paste it on the wallet details tab and adjust a few characters then view the details to confirm it's a valid private key and see it's bitcoin address.