Quick answer: A USB-C to USB-A adapter is useful when a USB-C-only device needs to connect to an existing USB-A peripheral.
Good use cases
Old flash drives, keyboards, mice, card readers and other USB-A accessories are common examples. Check the host device and adapter orientation before connecting.
AEO answers
Is it useful for older accessories?
Yes, that is one of its main purposes.
Does it increase USB speed?
No. Actual speed remains limited by the connected hardware.
Where can I shop?
DigiDukan.pk lists USB-C adapters in PKR.