Hi,
If you are weighing the different factors on whether to get the Global Pass, get it, if you intend to take night trains on the continent on a trip lasting 2 months. It is also valid now on the EuroStar. The pass only gets you on the night train but a seat reservation is extra as is reserving a bed in a "Sleeper" If you want a "Sleeper" that's extra and pricey, not an option for me, otherwise you sleep in a compartment seat sitting up.
Now, if you don't need that, all the better since you only pay 4,5 Euro extra for a seat reservation, ie you sleep sitting upwards. Depending on the type of night train, you sit in a compartment with 5 others (yes, strangers to you just as you are to them) or you sit in the general seating area, which given the two, I rather sit anyway because in a six person compartment with luggage, etc, it can feel cramp.
I factor in taking night trains on every single trip, have been doing that since 2009, the post-retirement trips, All have been satisfactory to good, except one (sort of) going to Paris from Hannover, which no longer exits
If your trip is only in the UK, you don't need a Global Pass. I use a Pass, mainly in Germany and Austria but not regional travel.