Most mail does not deserve to interrupt you. Everything lands in one list, nothing is filed on a guess about who sent it, and two piles keep your inbox from doubling as a to-do list.
Fifteen seconds: one list, the keyboard, a conversation, and the two piles. Every message arrives in the same place and nothing is sorted, filed or held back on a guess about who sent it. A conversation is a single page, oldest first, with no quoted-reply chrome to scroll past. Reply Later and Set Aside are two piles instead of an inbox that doubles as a to-do list. You can forward your existing Gmail in and reply from the app, and those replies genuinely leave Google.