What’s the point of creative testing?

the other answers to this are great. To add to this - FB & UAC favour older ads with more spend behind them. The algortihms are designed to focus in on best performance - which is based on historical data, thus making it EXTREMELY difficult to scale new creative. FB/UAC will ofter actively murder it before it's had a chance to survive. This makes for a terrible long term strategy to fight creative fatigue.

I agree with the main idea: producing new creatives and coming up with very different concepts, frequently, and feed Facebook with enough data to find the winners, is key to improve performance.

Adding new creatives to the same campaigns and let old creatives die their beautiful deaths if they are outperformed, is a fast & efficient way to work, giving you imo 80% of the upside you could get with a cleaner test & analysis. It also you gives you the opportunity to have different creatives perform well together, for different mini-audiences within your big audience.

I find that shipping a ton of creatives, right when the ideas come to you, and empower everyone to do so in a team, creates a happy mess of results & let the truly best ideas bubble up.

Then after 1-2 months, dissect the results, slice & dice every dimension, clean up the mess and restart fresh campaigns with your top 2-3 ideas and a couple of variations. And let it compete with the old, messy campaign, which should slowly decay.

Managing a clean test environment, collecting enough data for a stat sig read, making sure the parameters/variables are the same, analyzing and sharing the results, can slow down the production quite a bit if you don't have a good PM. But if you have really good process in place and it doesn't slow you down, I imagine that's the holy grail.

In conclusion, I'd say that both approaches can work and to pick the one that fits your team style. And also your brand & budget (the bigger, the more structured you'll need to be, approval process etc.)

You answer your own question with this statement:

it results in non-trivial amounts of spend as Facebook tests that volume of creatives at the scaled budget level, or that constantly changing creatives in the scaled campaign might re-trigger the learning phase

To add an additional justification:

The purpose of testing in a separate campaign is that the poorly-performing test creatives will not adverseley impact the performance metrics of your live campaign, which would reduce its delivery. If the only creatives that ever touch your live campaigns are proven winners, then the average performance of your live campaign will be higher than it otherwise would be if you were testing unproven creatives with it.

Campaign performance history impacts delivery, so this is an important