In my opinion, 4 away rotations is too many for most applicants. The only reason why I would recommend doing more than 2 aways is if you are a below average applicant who really needs to boost your application and increase your chances at as many programs as possible. I don't want this to turn into a "What are my chances and should I do 15 aways" thread, so I'm going to focus on why I believe 2 aways is sufficient for the large majority of ortho applicants and let you make up your own minds. With that being said, there are a few things you should take into account about aways.
1) Aways are usually expensive - unless you have family/friends/etc who you can stay with, you must factor in housing costs, travel expenses, and basically anything else that you will need while away from home. For me, this averaged over $1000+ per away rotation. This was in addition to the rent, utilities, etc. I was still paying back home while I was gone.
2) Aways are usually more difficult than home rotations - this varies depending on school, type of rotation (i.e. trauma service vs. sports), and lifestyle factors. However, in general, you must adapt to a new city and hospital very quickly, always be on your A game with people you have never worked with, and always work as hard as possible. During my aways, I always put in more hours at the hospital than any of my residents by getting there super early to pre-round, staying late to finish whatever needed to be done, and taking call more frequently. This also doesn't include the time spent studying at home for the next day's cases.
3) The biggest problem with more than 2 aways is burn-out. You don't want to spend all of your time and money spending a month somewhere when you are burnt out. This will reflect poorly on your work ethic, attitude, and performance. I know someone personally and have heard many stories about people on their 3rd or 4th away in a row that are burnt out and don't do as well. I'm not saying this will happen to everyone, but it is just something to keep in mind.
4) You don't need more than 1 letter for your ERAS application from an away rotation. One of the main reasons for an away (in addition to impressing the program while you are there) is to get a strong letter of rec from someone at that program. This shows that not only do you work well at your home institution, but that you are able to adapt quickly and have wht it takes to be successful elsewhere. Sure, you can have more than 1 letter from aways or pick and choose where to send which letters if you have multiple, but 1 strong away letter is all you need. Plus, the ERAS deadline for letters is usually mid-October to the beginning of November, so you will be unable to include any letters earned after that point in your ERAS application.
This is just my 2 cents, but I hope it helps.