I would be honest, it is my first time to hear the term "synchronized movie". I even Googled the term with keywords "synchronized movie" and I didn't found an answer.
While reading the other answer, I realized you are referring to dubbed movies. Dubbing is a process by which the original actors' voices were changed by another person who provided vocals in another language.
Why do some movies were dubbed into the language of a country?
For example, in our country, movies in Spanish, Korean, and Chinese were dubbed into Filipino. Why? Filipinos generally do not understand those languages, and dubbing the words into our own language makes it easier for the viewers to understand the movie. However, English movies were shown with the original language and subtitle is not necessary.
In other countries, original voices were used, but there is subtitle. It is necessary for the viewers who cannot understand the language of the movie. In countries like China, there is subtitle of the movies whether in English or Chinese because it is a requirement in the country.
I am fine with dubbed movies because I can easily understand the emotions in the movie. I also love the subtitles. There are advantages of having the subtitles.
* Deaf people who can read can easily understand what's being said discussed in the movie. Yes, many deaf people cannot read the exact English sentences (I can tell because I am involved in sign language community) but the educated ones can read. Besides, it is rare that movies has sign language interpretations.
* It improves ones' reading or literacy. It will also improve your understanding of the words when being read in subtitles.
Therefore, whether dubbed or subtitles, both can be beneficial for the viewers.
I believe by "synchronize", you mean translate and dubbed the movies in the native language.
Reason behind dubbing is, dubbing the foreign movies into local language makes them more interesting for the native fans who don't understand the original language of the movie.
When any movie is translated into local language it changes the dialogues with local language's idioms/phrases/situations, which destroys the beauty of those dialogues and some of the movie lovers, who understand the foreign language above 90% level or to a good level wants to watch the movie in that language with its original dialogues and concept presented in any scene, but as they are unable to fully understand the accent or unable to catch up with the speed of dialogue delivery of the actor/actress, use subtitles.
Later was also the case with me when I started to watch English movies/series. I experienced the first case several times while watching any animated Hollywood movie (movie, I've already watched in English) dubbed in Urdu with the kids. It changes the original charm of several scenes and I don't enjoy them.
This is a good question!
Synchronized movies are easy to watch while reading the text on the screen can be a big challenge for some people due to slow reading.
Synchronized movies however can do a lot of damage. Let me explain.
Synchronization is not an easy job, there are many factors that have to be taken into consideration when deciding about translation. First of all, the synchronised text has to match the length of the original text, which could be a challenge. You can express something in one single word in one language and you might need two words to express the same in another language. I've seen many cases where the synchronised text was different from the original.
Synchronization takes away a lot of the original. You don't have that original feeling any more, sayings are changed to match the language and so on.
Watching synchronised movies can prevent you from learning the original language! I grew up watching movies with subtitles and has helped me a lot in learning English. My first choice is always the original language, I only watch synchronised movies in case I don't speak the original language and can't find subtitles for it in a language I speak.
And there's another aspect that needs to be taken into consideration. Subtitles can cost a whole lot less than synchronization! To do a synchronization, you need actors, rehearsals and redos in case things go wrong, while subtitration can be done by a fech people.