There's fewer drawbacks in 5 than there are in 4.4, as Atlassian have improved stuff and fixed bugs.
You'll need to be more specific in your question - what are you looking for? Asking for random "drawbacks" is not a useful question. Look in the issue tracker for feature requests that you think you might need, and for bugs that may affect you. Problems I might have with 5 are almost certainly going to be utterly different from the ones you may have.
Oh, and read the release notes and documentation too.
After reading your previous questions it seems to me that you want all others to do your work for you?! No accepted answers, no answers to other questions given or votes to those answering you. This is a community, not a "I'll ask the questions and you'll give me the answers". Based on previous posts I wonder if you have tried to look anything up yourself at all?
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