U10 relocation is required for all Wii trims. If not done, you will have boot instability problems. There are multiple ways to approach this:
1. The standard U10 relocation, as detailed in the Definitive Wii Trimming Guide (most recommended)
2. "Wireless" U10 relocation, which is not recommended for beginners but provides a cleaner and potentially more reliable install by bodging U10 directly into the U10 via and some other connections.
3. U10 emulation with PMS-2/Lite, which in my opinion should only be used in case you for some reason cannot do a U10 relocation (say you lost or damaged both U10 and U9) - there's some conjecture here, but from what I've seen the long U10 wire that tends to be created when using U10 emulation can lead to some boot instability problems or other issues. If you keep this wire short and secure it well so it doesn't break after a while, then it should be a valid option.
The video you saw where someone didn't do a U10 relocation is likely one where they used U10 emulation instead.
