Engadget's comparison of bike computers and smartphones suggests most casual cyclists can skip the dedicated device. A phone in a secure mount already provides turn-by-turn directions, ride logging, speed, distance, and elapsed time, and a smartwatch can add heart rate and sensor connectivity. The main advantages of a phone are cost and convenience, since riders already own it and can use apps for navigation and GPS recording.
However, the source identifies specific situations where dedicated hardware earns its place. Bike computers offer many hours of GPS and navigation without draining a phone, are built for secure mounting and water resistance, and include controls usable in rain, mud, or gloves. They also support power meters, heart-rate straps, cadence sensors, and rear radar via Bluetooth or ANT+. Offline cycling navigation is another pain point: Google Maps bicycle directions don't work offline, though apps like Komoot and Ride with GPS can fill that gap, sometimes with subscriptions or map purchases.
Engadget also notes that a bike computer doesn't eliminate the phone entirely, since some safety features still require a paired phone for data. The practical question is frequency: if preserving phone battery, all-day navigation, wet-weather controls, or dedicated sensor support are routine needs, a bike computer starts to make sense; otherwise, a phone mount, smartwatch, and occasional power bank may be enough.