Peak season (July-August in Europe, December-January in tropical destinations) means double the price, triple the crowds, and weather that's often worse than shoulder seasons. Off-season and shoulder season usually deliver better trips for less money — and the trade-offs are smaller than people fear.
The math comparison
Paris hotel, August: £250+/night, 1-hour queues for major sights. Paris hotel, October: £150/night, 15-minute queues, similar weather (often better — September-October is mild, dry). Same trip, half the cost, better experience.
Greek islands, August: €200+ apartment, beach packed by 10am, restaurants fully booked. Greek islands, May-June or September: €80-120 apartment, half-empty beaches, easy table availability, water still warm.
Where shoulder/off-season is clearly better
Most of Europe: April-May, September-October. Mediterranean: May-June, September-October. UK city breaks: April-May, September-October. Caribbean: November (after hurricane season, before peak).
Where peak season matters
Skiing: ski season is structurally winter. School holidays for families with kids in school. Specific events (Edinburgh Festival, Wimbledon, Glastonbury) tie you to dates. Tropical destinations during local rainy seasons (e.g., Thailand July-October).
Working remotely during off-season as a tactic
If you work remotely or can take work calls, shoulder season trips of 2-3 weeks (work in mornings, explore in afternoons) deliver the relaxation of a long trip without using all your annual leave. Particularly effective in Portugal, Spain, Italy, Greece in May or September.
Off-season and shoulder season travel is the highest-leverage travel hack available. Half the cost, fewer crowds, often better weather. The school-holiday constraint is real for some, but most adults can travel when crowds aren't there.