When/where/if:
1. Illustrations should be used.
2. Photos should be used.
3. IxD (interaction design) / animations.
4. Colour palette selection / creation.
5. Flourishes.
These are the things I struggle with when designing generic corporate marking websites. I'm not a designer but I've worn the designer hat many times. I always warn my employer/client that I'm more of a technical designer than a creative one. Nowadays I just stick to application design since it's 100% technical.
Example: as someone who's more technical than creative I could have come up with the overall layout of the Excalidraw+[0] website but I don't think I would have thought about adding circles around keywords or the dashed line that leads users down the page.