It takes approximately (again, as Tom said, it varies a lot from dog to dog) 3 years for a Havanese coat to fully grow. From a tiny puppy to a fully mature coat and from a cut coat to a coat where you can see no vestiges of the cut ends. So that's why people who show are very reluctant to have any hair cut. It means a LONG time out of the show ring if a dog is cut down.
But I've seen people go from a "puppy cut" to what, for them as pet people, felt like a full coat in a year or so. Anyone who knows Havanese well could see where the cut hair was growing out, but it was long enough to be really cute... just not something you could put in the ring. But these weren't people who were showing anyway, so who cares?
Just like people who never cut their hair, the hair on a Havanese will find its own natural length FOR THAT DOG (or person). Each will be a little different. Also, pet dogs who run in the woods and tussle with playmates (like my three) will certainly have more breakage than many show dogs being heavily campaigned, who often spend the majority of their time in an ex-pen, and heaven forbid that another dog touch their coat.
Not ALL show dogs are kept that way, but many are.
It is also incorrect for a Havanese coat to grow so long that it trails on the ground, so needs to be trimmed to keep that from happening. (as opposed to a Maltese or Yorkie coat, which is supposed to be cut off at ground level) But you see that in the ring all the time too. No dog is perfect. And if I had to choose a fault, I'd take a too-long silky coat over a puff-ball frizzy coat with too thick an undercoat any day. The too long coat is something that is easy for pet owners to manage. Those dogs from the puffball lines ALL get cut down in pet homes because they just mat too badly for pet owners to be able to manage it. Quite frankly, even in show/breeding homes, those dogs are generally cut down as soon as their show career is over.
You've all seen photos of Kodi many, many times. He never had scissors TOUCH his coat other than to trim his feet and sanitary area for 10 years. (until about a month ago) I've included a few photos that show Kodi's full, adult length coat, clean and groomed, but not with "conformation show type" care. Since I modeled his "puppy cut" on photos of him at about 10 months, I suspect that if I were to let him grow out for a year or so, many people wouldn't see much difference. A person who knows Havanese coats well would probably be able to see that it had been cut for another year after that. (But we'll see what happens. He's going to stay this length, at LEAST for the next few months
) But cut ends have a DEFINITE different look to them than ends that have grown out naturally. You can spot them easily once you know what to look for.
I don't think people should be afraid of putting their Havanese in a puppy cut. It is purely a matter of personal choice. So is whether that is done with clippers or hand scissoring. If it is done with clippers, it should be done with clipper guards, and not be too close a cut. If you don't know what you are doing, the first time have a professional do it and ask if you can watch. Scissoring is a lot more expensive, but if you want a longer puppy cut, it's the only way to get it, since even the longest clipper guard will only leave about 3". Hair grows, Havanese hair grows pretty fast. It's just that to get a SHOW coat, it has to grow a long way! To get a cute, fluffy coat takes a lot less time.
SHAVING, however, should be only in the direst of circumstances. When a dog has been so neglected that it is matted to the skin and usually is done under heavy sedation. Or if the dog has a wound or skin condition or needs surgery. In all cases, a shaved dog will need protection from both sun and cold until its hair grows out again.