When you are shooting a scene or subject over which you have no control, such as documentation of a workshop, event or performance that is not your own, then you will have to adjust your exposure settings based on the scene in front of you, matching the camera settings to optimise the light available to you and getting as close to your desired look as possible.
On a film set, the camera settings would be chosen first, then lighting adjustments are made to expose your subject optimally and with the desired look.
Lights can be added or taken away, windows can be covered, etc. You don't have to be subject to the changeable nature of the weather and you have much more visual control.
Theatre lighting would be another example of this, and can be adjusted when video documentation is a priority.
Shooting with natural light as your primary source, either indoors or outdoors can be beautiful, and it will be stronger than any light you can purchase, but is also unpredictable and subject to change, particularly in Ireland.
Controlled lighting can be more reliable for video, particularly when shooting for long periods of time or where multiple takes are needed and continuity preserved.
Additional lights can also be handy to lift levels to assist the camera, to clarify important visual details or to add atmosphere or character.
Dedicated video or stage lighting can be used, but even household lights or lamps can be helpful.