Some services are not really useful, especially if you use a desktop not a laptop. Examples of options to disable according to their usefulness. This Ubuntu tips show you How to Disable unnecessary services in Ubuntu :
sudo update-rc.d-f remove laptop-mode
sudo update-rc.d-f hotkey-setup remove
The service is apm, meanwhile, the energy management. If the apm command displays “No APM support in kernel” in a terminal, you can safely disable:
sudo update-rc.d-f apmd remove
If you do not have a PCMCIA card reader:
sudo update-rc.d-f remove pcmciautils
If your computer does not support Bluetooth:
sudo update-rc.d-f remove bluetooth
If you have an ADSL connection, services and pppd-dns dns-clean will do nothing. The latter are used primarily to manage connections from dial-up type (old dial-up modem).
sudo update-rc.d-f remove dns-clean
sudo update-rc.d-f remove pppd-dns
Finally, the rsync daemon is to keep that if you really need:
sudo update-rc.d-f remove rsync
Note that the command sysv-rc-conf to list all the services running on your system.
There are many other ways to optimize ubuntu, you can read it on other ubuntu tips articles.