A triathlon/TT bike is purpose-built for riding solo against the clock. It integrates aero bars so you can maintain a low, tucked position that slices through wind far more efficiently than a standard road bike. The geometry is also steeper, shifting you forward over the pedals to open your hip angle for better power output and a smoother transition to the run.
However, these advantages come with real trade-offs. TT bikes aren't designed for group rides or mass-start road races—they're actually illegal in most road racing events. They handle differently in corners and at slow speeds, and the aggressive position can be uncomfortable on technical courses. They also tend to be less versatile for everyday riding.
Choose a triathlon/TT bike if you're specifically training for and competing in time trials or triathlons, especially on flatter courses where aerodynamics matter most. If you're doing your first triathlon, ride varied terrain, or want one bike for both group rides and race day, you're better off with an endurance or all-road bike and adding clip-on aero bars.