Consistency is incredibly important when it comes to design but it must be used properly for a design to feel natural. There are four kinds of consistency: aesthetic, functional, internal and external.
Aesthetic is about style, appearance, colours, fonts and tone of voice. Helping build brand awareness and keeping the brandstrong and recognisable. Functional is of meaning and action. Buttons on electronic devices or the colour sequence on traffic lights all act and respond to how the user expects. Internal is being consistent with other elements within the same system e.g. wayfinding signage. External is defined as consistency withother components in different settings e.g. emergency signs.
Any brand, product or user interface correctly using consistency, will help create a more distinguishable, user-friendly, effective design.