As with everything, I guess do it in moderation and don't be stupid...?
Planning on being out a full day under the summer sun as a very pale north European? Slob on all the sunscreen that you can and hide in the shade when possible.
A day out in mid September / mid March when the sun is not looking to murder you? Revel in it. Soak it up. Be a plant.
Also it makes a lot of difference where you are. Scandinavians rarely wear sunscreen but their UV index is much lower than, say, California, let alone Australia.
Planning on being out a full day under the summer sun as a very pale north European? Slob on all the sunscreen that you can and hide in the shade when possible.
A day out in mid September / mid March when the sun is not looking to murder you? Revel in it. Soak it up. Be a plant.