Group use declarations shorten the import block

A file importing six classes from the same namespace repeats the namespace six times, which is noise that grows with the depth of the tree.

use AppBillingInvoice;
use AppBillingLineItem;
use AppBillingTaxRate;

use AppBilling{Invoice, LineItem, TaxRate};

// and mixed with functions and constants
use AppSupport{function format_money, const CURRENCY, Money};

It is purely cosmetic and it does have a downside worth knowing: a grouped import is harder to grep for, so searching the codebase for who uses TaxRate no longer finds this file by its import line. Some teams take that as reason enough to keep the long form. Either is defensible; mixing the two in one project is not.