I think the main reason is better antennas and thus more accuracy (and probably longer battery time, though that's probably only relevant for handheld use, not in a car).

Some dedicated GPS include a service which pulls up live traffic information and calculates the best route based on the current condions, e.g. to avoid getting caught in a traffic jam or having to do a u-turn due to roadworks.

Very related question on TGO: outdoors.stackexchange.com/questions/8439/…

A dedicated GPS cannot broadcast your location

A small reason, but having two device means two batteries. Your phone won't die if you're using the GPS constantly, and your GPS won't die if you're on the phone all the time. This is somewhat mitigated if you only use GPS in your car and keep your device on charge at all times while in use.

@angussidney: you seem to be describing Waze, as installed in my phone. Google Maps also uses traffic information to calculate its routes.

You are mentioning a car. Do you mean specific for car navigation?

@Itai: it's all about having the right tool for the job. My phone has a camera, why would I buy a DSLR? My phone has an office suite, why would I buy a laptop with Microsoft Office? And so on. If the phone app does well enough for you, then use it, and if not, use something better suited. My old TomTom sits unused in the car, in favour of 4G + Google Maps on my phone, but when I'm hiking I'll take a dedicated Garmin unit that can run on replaceable batteries, and a shockproof/waterproof Pentax camera, and save my phone's battery for emergencies.

@flith - That is the question! I know why a DSLR is better than a phone... but I don't know why a GPS is better than a phone (if it is).

@Itai: I'm not sure why FighterJet's answer is getting the most votes, because the one posted by Burhan Khalid covers the pros and cons pretty well. But if your use case is standard point-to-point driving, I'd tend to suggest there's little added value for you in using a dedicated unit. I use my phone on long journeys for pretty much everything navigation and music related.

For in-car use one should perhaps also not forget the disadvantage both a dedicated GPS devices and a phone/PC GPS has compared to a third category: a car's built-in GPS navigation system. The latter may still be able to follow a road system under ground (tunnels, buildings) by utilizing the car's sensors, while the other two drops out when the GPS signal is lost.

Depends on what you use it for also. Your question suggests navigation in a car. Since Apple Maps has no "bike" setting, I use "walk" to get the shortest route. As soon as I reach ten kilometers per hour, the stupid thing assumes I am driving and recalculates a different route.

@Martin, a stand-alone GPS is a dedicated satellite navigation device for your car. It usually sticks to your windshield with a suction cup and has a 4.5" to 7" touch screen. Common manufacturers are TomTom, Garmin, and Magellan.

are we talking about a car GPS?

Any device that serves only as GPS. Most of them are designed for cars I guess but I'm sure someone can come up with a different example, maybe portable to be usable without a car.

@njzk: The question asks about using a GPS while in the car, so yes. Trail GPSs (for use off-road) are another whole class of devices.

@ltai: While some car GPSs do have a "walking" mode, that's a secondary purpose, and I've never actually seen anyone use one for that. Most people would just use their phone.

When you say "only as GPS" you may want to clarify that you mean a navigation system. "Only GPS" to me means literally it only tells you your position - the maps and navigation aren't part of the GPS system, they just use the position it gives to help you navigate. I don't know if there are local usages of the term that mean GPS means satnav system but to me GPS means literally just the positioning system which is why I was very confused by the idea of replacing the satnav on your phone with one. :)

Fwiw, anecdotally, I have far more stability issues with software on my phone than with a reliable dedicated system like a Garmin. Also the dedicated systems generally have the maps right on them so you don't always need an internet connection. And I find that at least Garmin's UI is much preferable to me than that of Google Maps, Waze (since their UI update a few years ago), Verizon Navigator, etc. On the other hand the realtime traffic/construction/accident updates of e.g. Waze are pretty nice to have.

There would seem to be a localisation/terminology issue that has confused some people... in the UK, for instance, "a GPS device for your car" is universally known as a "Sat Nav". Whereas a "stand-alone/dedicated GPS" device would be considered a "Trail GPS" (that @FighterJet mentioned).