Lots of people brought good points already.
It's not really glamorous to tour and depending on how much you tour, how far you reach (regional, national, international) and how big is your show, there are different hurdles.
Since your question is about bigger overseas tours and the like, let's run with that. There are different concerns.
Routine: Forget about your normal life. if you're the type who enjoys waking up at the same place and doing exactly the same thing in the morning and have your little rituals during your day and taking the same path to home every evening, touring is not for you. Lots of people will feel homesick, even after a 2-week vacation.
Family and loved ones: This will take a huge toll. If you have a wife or girlfriend, expect this to be a big challenge on your couple. If you have children, this will also be torture. You will be missing huge chunks of their lives. You will also face the possibility of being absent when these people need you the most. Your dad is the hospital after a heart attack, your wife is growing increasingly distant and had befriended the asshole at the sales department, your son is struggling at school with bullying and a learning disability or your 15 year old daughter is at risk of getting knocked up by a local wannabe gangsta? Tough shit, you've got a gig in Athens tonight and then you're off to Scandinavia for the next two weeks.
Friends and band mates: Some of your friendships will be tested. You won't be there for them and they won't be there for you. Some friends may become distant. If there is friendship between band mates, this will be put to the test by the proximity. Infighting, jealousy... some people start literally hating each other. You're stuck with those people in enclosed space for long stretches, you may have to suffer their moods, opinions, egos, etc... this is exacerbated because like you, they are going through the hell of this long list I am making.
If you have no loved ones and few friends, you're avoiding a lot of those issues but you have no network. Forget having pets or plants... your main issue will be finding where you sleep or who picks the important mail home. That's if you have a home. I've known roadies who basically lived a lifestyle close to itinerancy. They disappeared off the map and came back years later with basically no home and little possessions except what they were carrying. They have to start over their lives from scratch.
Other than those personal concerns, there are three other very important types:
Legal: The world is a really strange fucking place. You will absolutely want to avoid getting in trouble. You may not even know it when you are breaking the law because you've been programmed a certain way by your surroundings. Some legal systems are totally alien and scary as fuck. You will not have the benefit of being a citizen. A tour that was supposed to break even can cost you several thousands of dollars in legal fees or ass-fuck you to a dirty jail where they have a vague notion of what exactly are human rights. If you have a criminal record, expect even more hurdles. If you're a regular drug user, be very fucking careful.
Professional or educational: The more time you put as a musician, the less time you will put in a career or education. It is not likely that your career will make you rich and famous and last a long time. You will need to plan appropriately. Ironically, you'll never need as much money as while you're a musician.
Medical: You know how many people go on a 1 or 2-week vacation in an exotic resort and come back stressed out, extremely tired and sometimes really sick? Well, touring is like that but ten times worse! You will be constantly jet-lagged, eat things you're not used to. Your body and mind constantly adapting to new surroundings. I can't stress this enough. If you have already have a medical issue or recurring health problems, touring may make your life a living hell. I have a friend who is a doctor at a clinic specialized for travelers. There are horror stories that have taken lives or changed them forever.
Basically, touring it's not what it is cracked up to be most of the time. It's expensive and everything that could go wrong in your life leads to extra difficulties when you're on the road. You will want to be insured and take every precaution every step of the way.
Naturally, there are ways to make touring a lot better, especially if you don't do it extensively and leave room for a personal and occupational life. You have make smart choices and you'll probably sacrifice career goals in order to have more of a "normal life".
Meh, cry me a river....What you are speaking about is the price of fame and living one's dream. If you get lucky, and have the talent, just maybe it will pay off, and, if not, well then you are either worse for the wear or back where you started. Now, I realize in the extreme metal realm, living off a band is much harder than say living off a pop band, but we've all known this for years. I mean I've had many well paying jobs that absolutely sucked the syrup out of a maple tree, but provided me with stability. I can't say though that I've seen much of this country, or the world for that matter, like band members say in a band like Napalm Death. There are trade offs in every aspect of life.