The requirement in the Building Regs for an extract fan in every kitchen, utility, bathroom and shower room is there to make sure that the moisture vapour is removed as close to the source as possible. Cooker hoods that don't extract steam directly outside, from boiling water and cooking, leave all that warm vapour in the house or flat which then condenses on any colder surface, usually under furniture, inside wardrobes and on external walls. Over time, without alternative ventilation these damp surfaces may start to grow mould and encourage wet and dry rot.
So, always fit an extract to outside air in a kitchen , over the cooker hob at the source of the water vapour. Or, wherever you can in the kitchen, as close to the hob as possible.
People don't ventilate their rooms as much as they should because they are concerned about losing heat, if you have the chance put in a heat recovery unit in which recovers up to 90 to 95% of the heat from extracted air from kitchens and bathrooms across a heat exchanger in the unit providing warmed fresh air into living rooms and bedrooms [bit more ducting required but it's worth it]. The heat recovery part can be turned off in summer when you want to cool your kitchen down.