Any sort of integration, but some can be broken down into steps more easily than others. About a decade ago one of my roles at the startup I was at was keeping our browser built atop Chromium up-to-date with Chromium trunk. I normally would merge in all Chromium's changes each morning. Some weeks I just had other stuff to do and so it would be a full week I'd gone without merging.

Merging a full week of Chromium changes in all at once was just too many merge conflicts to deal with.

So I'd simulate as if I'd been merging daily by just doing 5-7 separate merges, which worked out well enough.