Access to the EU single market (500M+ consumers), free movement of goods/services, common agricultural/fisheries policies.
Voice in EU decisions, common foreign/security policy, Schengen border-free travel.
Adoption of high EU standards in environment, consumer rights, social policy.
Citizens can live, work, study across Schengen Area; boosts tourism and cultural exchange.
Greater diplomatic weight, participation in EU policy-making, stronger representation in UN/WTO.
Obligations (EU laws, budget contributions) were seen as outweighed by benefits.