CMS websites aren't always a walk in the park though, and if you don't know what you're doing, the weirdest things can go wrong in the weirdest ways - and those issues can land up affecting your online sales, the information you gather and more.
Apart from the fact that they save you time redeveloping the same basic features with every new website, CMS websites have the added benefit of keeping your website current through future browser updates - for years to come - which means your website won't need to be replaced as often.
However this only works if you keep your updates up to date - and that is an ongoing process, with new updates often arriving every week.
Past a certain point of lapsed updates, it actually becomes not feasible to update your website and you'd be better off rebuilding it. So updates is not something you can let slide either, because then your CMS system is as much use to you as a website you can't update.
Sometimes the developer put in custom CSS, sometimes there's been a change in the way code talks to each other because of an update; whatever the reason, if you run updates on major plugins and components, then you need to check through every major process on your site as part of the update process.
As an example, you could update a cart component and find that your 'thank you' page is no longer rendering correctly and people won't be able to access their account profile or downloads. Whenever you update any component on your site, you have to check the functionality affiliated to all the major components - because their coding can conflict each other too. Those conflicts might only arise after an update.
So if you have a store and a membership subscription section and forms on your website and you only update the forms component, you still need to test your forms, as well as do a test run through of your subscription and cart sections. Sometimes these conflicts are permanent and you will have to find a new component that does not conflict with the system configuration you've created.
Speaking of weird stuff that affects things in weird ways... multiple templates can generate strange results too. It's always worthwhile checking your system-generated pages like carts, subscriptions and forms after making changes or assigning different templates. The weirdest glitch I've seen so far is that by default Joomla will open any article not assigned to it's own menu item in the home page or the category blog it belongs to. This means that this will apply to system-generated pages too.
So if you apply a different template to the home page, which is a common occurrence, that template will then apply its CSS to the system-generated pages, instead of calling the default template's CSS, making your text not visible against the background or changing the background colours of form fields, for example.
Also show on all pages except those selected is a really useful tool unless you have components that create system-generated pages. Many of these pages will need to span the width of the full page and their overflow won't be hidden, so any elements that you've left to show on all pages except those selected will appear on generated pages, and can adversely affect the display of those pages.
Free extensions and plugins are great if you are working on a limited budget at first, but beware that they come with hidden aspects that make them either annoying or dangerous. Some of them are downright dangerous with links leading back to sites or driving traffic to undesirable sites. Others just make it very difficult for you to work with them.
So you get enough functionality but it's limited in how many pages you can apply it to, or will have a limitation in terms of configuration and styling. If you really like the component it's worth paying for the license. Most licenses will cover your updates for the lifetime of the site.
The most amazing technological feat of CMS websites is the mobile responsiveness that the template provides - your website should work across browsers and devices pretty flawlessly.
However you need some basic development knowledge and theoretical understanding in order to utilise this to its maximum potential.
And here's the one that people really forget about the most: you need to look at the site on a mobile device - as many mobile devices as you can lay your hands on in fact. The only way to see what really works and what doesn't is to look at it - in every possible configuration.
