If you need to warranty repair yes, it can be a problem. Although technically Core Group is supposed to honour Apple's international warranty here. But as we all know they're a bunch of crooks and will find every excuse to con you.
I've imported about 3 of my iPhones, and around 6 Macbook's over the years (also some Dell and HPs) and have never needed to send one back.
In fact ironically, the one iPhone I did have to get repaired was an MTN contract one from South Africa and I was in the US for work and it broke and i went to the Apple Store and that was the first time i realised the contract between here and there.
No red-tape and excuses and nonsense like iStore South Africa shops - they took the phone, i told them whats wrong. She said oh dear, this can't be repaired in time for your stay in the US, can we give you a not-for-resale swap-out device instead? i walked out with another working device in 30mins and someone in my family is still using it many years later.
At least 3 times i've walked into an Apple store in the US as a foreigner - told them i'm a foreigner and my device is not from the US (once above, the other 2 times I broke it myself, don't ask..) and every time they made me feel like i had purchased it from them and were super glad to assist.
I come back home and walk into an iStore and its such a disaster or incompetence and crooked dealings to try avoid fixing anything that I just have to stare in amazement.