Some prefer to use managed solution as this way the customer will not be able to change the solution attributes that the developers have added. Some don’t think like that as they tender to think about the advantageous that using an unmanaged solution would give.
I would prefer having an unmanaged solution in the development and managed solutions in the UAT and Production environments as it would keep the control in our hands. However there are pros and cons to this as well.
There is a great article that has been written by Gonzalo Ruiz regarding this topic of managed and unmanaged solutions at the following link.
Also he has written another nice article about deleting an attribute from a managed environment in the following article.
Both these articles are great articles to read if you are person working with CRM. This would give you some insight of how the things are happening and how you can cope up with them.