I'd never used a GPS of my own until that particular day - it was a wake-up call! Now I always use a GPS app and a GPS route on my phone. But I always carry a map and compass too, because I generally find them more useful. I use the GPS app as back-up or to check altitude.
GPS can sometimes be slow or even fail - this can happen in cloudy weather. I've also been on hillwalks where someone has been following their GPS route, and it's not exact, so we were taken all over the place - up hills, down hills, in one direction and then back in the other direction... eventually I took a quick bearing on my GPS, and I could see from it that we needed to be heading direct north. The person who was actually following their GPS was taking us west, because it was cloudy and the arrow was pointing that way for a bit, and then another way... I spoke up and said that actually we needed to be going directly north, in the direction my compass was pointing. We went that way and within minutes we could see the path we'd been trying to find.
Also, GPS batteries can fail. I'm not against them - I use mine periodically, to check that we're on the right track. I think you're unlikely to go wrong with a map, compass and GPS.