HI Alicia. CUCM and VCS can provide call control, alias or numeric dialing etc. It can also control BW between nodes and regions if restrictions exist etc. VCS and CUCM would be nice to have, but if you have a small deployment, maybe using the on board GK on the MCU may do ok for you for now. If the organization grows, and you have a mix of H323 and SIP devices, and then have a need for FW traversal, VCS Control and Expressway will help in this area.
Basically, I would think on how the organization will grow, and if it continues to grow at a good pace, then having call control device like VCS and or CUCM may prove to be quite useful.
Hope this helps.
VR
Patrick