What are the advantages and disadvantages of conducting some governmental matters in secret ?

Some of the advantages of the conducting governmental matters in secret is that matters at hand can be dealt with accordingly without the interference of other people. Also, plans can be properly lay-out first before communicating it to the public. 

The disadvantage would be there could be limited opinion regarding the matter and hand. Consequently, there would be limited access to ideas as more people could have generated more. 

The east end of the national mall