Questions About Wether You Need Studio Light On Location
I think it’s a very important practical question, especially for people who don’t have they own studio equipment, but have to rent it for the occasion. Or for people who don’t have a car and afraid to transport the light in public transport (if you do it try to avoid rush hour). Or for people who organize a photoshoot in another city where they need to get by plane (all your equipment will be returned bent from the luggage). Or when you are working in National Park and lighting requires much more pricey permit.
There are two different cases of the situations when you need the light: it’s too dark or the “local” light quality is too bad. First case would be train station or forest during overcast, or tunnel or cave, or inside the building with very small windows — just visit the location beforehand with your camera and you will see if your lenses can handle the amount of light you will find there. Here you can use flash or constant light and you just need enough to have acceptable grain and focus.
Second case is way more nasty. Some examples of it are yellow electrical light, ceiling light, certain types of forests in summer, very narrow street and street lights after twilights — here, even if you have enough light (high ISO, small depth of field) you will still have unpleasant shadows of the face and bad color in the shadows too, so you need your studio light to be strong enough so that “local light” wouldn’t make any difference which means you have to use flash and on big brightness too.
In general you can either spend time and effort bringing light in or finding good spots on location. But it will be harder to find a spot when both light and backdrops are good unless you have a lot of experience with it.