Boris Cherny, who built Claude Code, runs terminal sessions in parallel, each on a separate branch. A task that takes hours in sequence takes hour when the subtasks run at the same time.
The key is decomposition. Split a feature into independent subtasks where each touches different files. One session works on the API layer while another handles the UI layer.
The rule is strict: never assign two agents to the same file. Overlapping edits produce merge conflicts that cost more time than the parallelism saves.
I open each worktree with claude -w, assign a focused task, and check back when each session signals completion.