Maybe it was done by design, but consider the 'expense' of getting shipping methods/rates. I.e. imagine getting rates 'by warehouse' and also using multiple shipping providers (e.g. UPS and USPS).
1. nopCommerce version 4.30
2. Expected behavior - ??
3. Actual behavior - every keypress when typing in the zip code field makes a call to Get Shipping Options
4. Steps to reproduce the problem
Select "Estimate Shipping" button on the cart page. The dialog pops up.
Enter characters in the zip field (Also changing the Country or State/Province)
Notice the delay ;) but better, set a breakpoint in the shipping service to see impact.
Also, if using a provider/carrier that's expecting a valid address, like UPS, you will see errors in the system log - e.g.
Hard error: The requested service is unavailable between the selected locations.