englishal,
Vfr details are often passed onto adjoining units by ATC. I always like to give my colleagues a "heads up" on what traffic is going to transit through their airspace.
However, wether or not I have time to pass on these details is another matter. As a radar controller my first priority is to sequence my ifr a/c and provide a service to my RAS a/c. Next in line is a/c under a RIS and last of all to a/c under a FIS.
If I am busy with other a/c then, I am sorry to say, it is the FIS a/c that will lose out and passing vfr overflight details to another unit is very low priority, especially when as all ready stated, there is no requirement for such a/c to contact the next unit if in class E/F/G airspace. Numerous times i have passed vfr details only to tell the a/c to "contact xx" and to be told back that they are changing their routing and going to contact zz instead. Not only is it a wasted phone call in the first place but then you have to call the adjacent unit again and tell them to bin the details!
Even if you do have the time to pass on details, the receiving unit may not have the time to copy them. If you are busy the last thing you want to do is take a phone call with such details and often you will just tell the controller to tell the a/c to freecall.
If you file a vfr flight plan before departing then all units along the way get details through the AFTN system and this again reduces the details you have to pass. There is nothing worse than a pilot giving his lifes history on the R/T!!
As already stated even if the R/T is quiet it often means that we are on the phone. We have to do a lot of coordination for both vfr and ifr flights. Phones are constantly ringing in my ears, but a phone call in my opinion is much better than trying to do such coordination over "electronic methods". At least with a phone call you know that coordination has been effected and that everyone knows what is happening. That way things stay safe which at the end of the day is what its all about.