During the Clone Wars, the Galactic (Republic) Senate was slowly stripped of its powers in favor of the Supreme Chancellor (Palpatine). At the end of the Clone Wars, Palpatine transformed the Republic into the Empire and declared himself Emperor, but he did not disband the Senate immediately. Instead, it became the Imperial Senate.
What were the powers of the Imperial Senate? Did it still have legislative and executive powers (and perhaps even limited judicial powers) as the Galactic Senate did (albeit subject to the Emperor)? Did it have any level of control over the Imperial military? Or was it reduced to nothing more than a purely advisory council?
In Episode IV, Tarkin hints at the powers and functions of the Imperial Senate just before it was disbanded:
Tarkin: The Imperial Senate will no longer be of any concern to us. I've just received word that the Emperor has dissolved the council permanently. The last remnants of the Old Republic have been swept away.
Tagge: That's impossible! How will the Emperor maintain control without the bureaucracy?
Tarkin: The regional governors now have direct control over territories. Fear will keep the local systems in line. Fear of this battle station.
This implies that the Imperial Senate somehow helped the Emperor maintain control via "bureaucracy", and that it had some control over Imperial territories. However, it also implies that there were regional governors who presumably had some control over Imperial territories as well. How did the Imperial Senate share power over Imperial territories with the regional governors?