It sounds silly, but time zone difference is probably one of the more challenging ones I’ve encountered.
For us, corporate headquarters is in the East Coast, but most of our Execs are Pacific. When we acquired a company in Europe (GMT+1), most folks didn’t adjust their working hours… which meant that meetings could only be scheduled between 9am and 11am Eastern time without getting pushback from one group or another. When the US and Europe diverge on Daylight Savings Time (given that these now occur at slightly different dates), it wreaked further havoc on figuring out exactly when meetings were taking place.
Knowing who’s going to be responsible for taking those early morning / late evening calls seems obvious, but in practice, your corporate culture may be less supportive of that than you realize…