A simple rule: familiar and simple can be DIY
A good way to think about it is this:
If the trip is familiar and simple, DIY planning often works fine. That might mean a destination you already know, a short hotel stay, a road trip, a simple beach trip, or a place where you already understand the logistics.
If the trip is unfamiliar or complicated, help may be worth considering. That might mean multiple rooms, a cruise, an all-inclusive, Disney, a multi-stop Europe trip, a destination you have never visited, or a trip where a mistake would be expensive.
The line is not really “DIY or advisor.” The line is familiarity and complexity.