You can call it FOMO (fear of missing out), with a dash of “don’t tell me what to do” rebellion, but I like to have some say in how my time in spent when I travel. Spontaneous travel can work on its own or mixed in with activities you’ve planned.
I generally want to have some ideas for what to do and where to spend my time, but I don’t want to follow a rigid schedule. What if I’m checking out a cool museum, or heading to a restaurant and see an interesting looking street with lots of great-looking shops down it? I’d want to have the flexibility in my day to be able to wander around for a bit.