• Top-quality camera
• Solid battery life
• Near-stock Android
• Fingerprint sensor
• Headphone jack
• Relatively cheap ($300)

Several years ago, phones got good enough at most things that the extra money for a "flagship" phone [1] felt like it didn't make sense. What held me back was the camera: I take a lot of pictures and really enjoyed how much better phone cameras were getting. The 3a changed this: it has the same excellent camera (and camera software) from the Pixel 3, decoupled from the other choices that made the 3 expensive.

In general the tradeoffs on the 3a are ones I'm ok with: it's a bit thicker, the back is plastic (which I cover with a case anyway), it doesn't have wireless charging (which I don't use), it has a slightly slower CPU, it doesn't have an ultra-wide selfie camera (which I wouldn't use), isn't water resistant, and has slightly less fancy glass. On the other side, it has a slightly larger screen, a slightly larger battery, and a headphone jack.

The battery life has probably been the largest immediate improvement for me, but that's mostly just going from a two-year old phone to a new one. Still, it's pretty great having 50%+ battery left at the end of each day.

The other thing I've noticed is a pretty minor UI thing: holding down the camera button takes a video instead of a burst. While I'm not sure what this means for my kids' pages it is really convenient when I want to jump right into taking a short video. It's possible that there's also some sort of hardware change that enables this, since I remember previous phones taking longer to get into video mode.

Overall I'm very happy with it, and would recommend it to other people who see the tradeoffs involved the same way I do.

(Disclosure: I work for Google, who makes this phone)

[1] My past phones, all the cheapest version of the flagship phone from their manufacturer at the time: Galaxy SII, Moto X, Galaxy S6, Pixel.