But if tanning also produces cancer it remains to be determined which effect dominates (unlike for people with naturally dark skin, where the effect can only go in the beneficial sense).
https://www.scientificamerican.com/article/fact-or-fiction-a...
You clearly get more than SPF 3 with a deep tan as you can spend 8 hours in direct sun without obvious problems. Without any tan you get a burn in under an hour suggesting ~SPF 10+.
For a fixed amount of sun exposure, spreading out the duration is better both to establish a tan and to allow more time for skin recovery. But there isn't really a case where tanning increases safety, because you get the tan via exposure.
It's like saying pilots who practice a lot are safer; for any given flight it might be true, but cumulative risk can only rise.