What are the benefits of the Segwit upgrade?

TLDR: Segwit enabled the Lightning Network and increased block size from 1MB to ~4MB.

Details:

Segwit fixed transaction malleability. It did so by moving the malleable part of the transaction, the signature, out of the main block into the coinbase section. Fixing this issue allowed developers to deploy the lighting network as a layer 2 solution.
By moving parts of the transaction, i.e. the signatures, to the coinbase section, Segwit effectively increased the blocksize limit from 1MB to ~4MB
Segwit enabled a clean way to deploy future soft forks by implementing a script versioning system. Segwit uses version 0 and Taproot uses version 1.
Hardware wallets were vulnerable to a form of attacks where a malicious actor could trick the wallet into signing a transaction that excessively spends on transaction fees. Segwit transactions fix this vulnerability by having hardware wallets signing a combination of input utxos plus the input utxo amounts.