What each time control trains
Blitz (roughly 3 to 10 minutes per side) trains real decision-making: you have time to calculate short lines, evaluate trades, and recover from a bad position. Most coaches consider it the fastest format where genuine improvement transfers to slower chess.
Bullet (under 3 minutes) trains pattern recognition, mouse speed, and clock handling. It sharpens instincts you already have, but it rarely builds new ones, because there is no time to verify a new idea.
The common trap
Many players grind bullet because it is exciting, then wonder why their classical results stall. Bullet rewards habits — including bad ones. If your habit is moving before checking for threats, bullet gives you thousands of repetitions of that mistake.
The reverse trap also exists: only playing slow chess can leave you helpless in time scrambles, which decide a large share of blitz games.
A practical split
A simple structure that works for most improving players: use blitz as your main competitive format, use rapid or training games to learn new ideas, and treat bullet as entertainment or endgame reflex training.
Whatever you play, review it. A blitz game followed by five minutes of analysis teaches more than ten blitz games on autopilot. Gambet keeps every game with automatic engine analysis, so the review step costs you nothing extra.