Buying crypto through exchange vs wallet

Hello everyone, I'm new to the crypto world and this might look a bit dumb at the eyes of the experienced but I'm trying to understand what is the point of buying crypto directly on an exchange if you can do it through your wallet of choice and vice-versa.

When it comes to fees, I'm aware Binance has a 0.1% fee for each transaction and I have already invested some money there since May but wouldn't it be "cheaper" to purchase any crypto via wallet since technically you'd only pay the network fee for the selected coin?

Thanks