I have to agree with the poster above, when you have a number of websites it makes updating so much less painful.
This is weird question, obviously plenty of open source cms are very powerful scripts with great abilities that you wouldn't be able to code alone. Drupal, Joomla, Wordpress are the results of work of many people.
Yes, this is true, but the question is "Whats YOUR purpose for using a CMS" In other words, whats your reasoning for using a CMS over conventional html/css?
cms's have simple admin panels. after designing the website I give password to buyer. they likes to walk in the administrator panel
It's not so much for me, but for scalability. Imagine you start a great website and you build it from the ground up, being able to edit articles with a backend CMS makes it so much easier than editing code. Granted I know how, but let's say in a few months the site starts to get popular and I look for guest writers or hire others. They may not know how to code, so having a CMS makes it easier on everyone