What is a 'wysiwyg'?
A what you see is what you get, website builder is simply that. You are only able to use the tools within the proprietary builder, in order to quickly push out a website, with little to no understanding of anything code related. At a previous job, we would have specials on these that averaged out to about 600 bucks, but we also included SEO. The prime reason being that it was super easy for people ( like my dad ) to figure out how to manage it. Is this the best route? No, definitely not. In fact, those clients I had previously would oftentimes be calling their sales agent to have stuff done on the site. Again, not something that is very user friendly. While I do see how some folks can utilize these drag and drop builders, ultimately their lack of customization leaves everything looking the same.
During my time in web development
I sat there customizing the back end of Weebly, throwing parallax into different sections, just with CSS. I will agree that it was pretty fun making this proprietary software do anything I wanted it to. However, from a practical sense, I found it to be quite scary. I moved on to lead the on boarding of the Website Builder team, post web development. This is when I started to be quite annoyed with these drag and drop builders. I would oftentimes get customers who wanted to move their sites to a new web host. Nope, that was the answer. Every. Single. Time. Now as a professional in the industry, if you pay someone to build out your site, you expect to take it to a new host, should you be displeased. Not with 'wysiwyg's. This is a sad but true tale. You don't want to be at the mercy of whoever owns that entity. EVER. I cannot stress this point enough. I've seen it time and time again. Whether you're utilizing wildcard SSLs, need additional server capability, or anything in between, you will be at a total loss.
Drag and drop has it's purposes
It's excellent for the do it yourself business oriented person, who has to get some information up and on the web. It does not take the skill as developing a normal site. If you're a beginner, the drag and drop is the way to go. I highly recommend it for people who are starting out. If you're like my dad and can't figure out a DVD player, go this route. You can eventually work your way into a CMS with enough practice!
Content Management Systems and You.
There is a plethora of CMS's out there. Some examples are Joomla, Drupal, and my personal favorite Wordpress. So what makes these different than your regular proprietary builder? They're all content management systems, created with consistent updating in mind. They all utilize PHP driven databases in order to serve you content. What makes this so special is that most of the items developed for these platforms were made via open source. This brings together an entire community in which fantastic things happen.
Cons
Oftentimes, CMS platforms tend to go out of date, and end up breaking. This isn't a problem if you research the issue enough. In fact, fixing it yourself will teach you at a much faster rate. You will learn PHP, different functions and maybe a ton of SQL queries in between. This will make you much more versatile. The truly bad part of any CMS is the learning curve. You never know how much time you'll need in order to master it.
Functionality
You can customize these until you lose your mind. If you get well versed enough in PHP, you can even start making your own themes or plugins for others to utilize ( Open source for the win! ). You can take your site to most hosting providers ( Portability ! ). If you are willing to learn the ropes, there is not much you can't do with a proper CMS. There are some other options out there, but for the SMB ( Small or medium sized businesses ) a CMS will serve you well 90% of the time. From someone who has worked with both for SMBs, remember, there is a time and place for a wysiwyg, but you should try to learn the way of a CMS!