What is a potential drawback of using a handheld VHF transceiver inside a vehicle that lacks an externally mounted antenna?

A vehicle's metal body acts as a Faraday cage, meaning it effectively blocks, absorbs, or reflects electromagnetic fields. When you transmit or receive using a handheld radio completely enclosed inside a car, the metal structure acts as a shield, drastically reducing the amount of RF energy that can escape or enter the vehicle. Using an externally mounted antenna completely eliminates this issue by placing the radiating element outside the vehicle's metal shielding. The metal roof or trunk can then actually benefit the system by acting as a highly effective ground plane. While operating inside a car might cause minor detuning of the handheld's antenna, it will not instantly cause the radio to overheat, nor will it inherently decrease the SWR. The primary and most noticeable drawback is severely degraded signal strength.