Expression is usually through liquid instruments: futures, forwards, swaps and options, which lets a manager put on and remove large exposures quickly. Positions are often asymmetric by design, using options so a wrong view costs a known premium.
Discretionary macro depends on a small number of large calls, so returns are lumpy and dispersion between managers is wide. Systematic macro applies rules to the same markets and behaves more like managed-futures.
The recurring risk is that a correct thesis arrives late. A position sized for conviction rather than for the path can be stopped out before the view plays out, which is why macro books are usually built around position-sizing and predefined risk rather than around certainty.
Related: managed-futures, trend-following, position-sizing, hedge-fund, risk-on-risk-off, carry-trade