I'm a huge advocate for using WHMCS and I understand how powerful is WordPress for content creators but I still think that using both systems together is a terrible idea for a number of reasons. Before we start analyzing them, I'm taking WordPress just as an example but my points are valid also for Joomla, Drupal or any other CMS that comes to mind.
DistractingIt's already difficult to keep an eye on the admin interface of WHMCS, servers, control panels and registrars. With WordPress we're adding another system to monitor on a daily basis. That's distracting and not really necessary.
Twice the loadThere are countless things that can go wrong in WHMCS and WordPress individually. Combining them makes things even worse. They both requires updates, have vulnerabilities, different structure and most importantly specifications and requirements change over time forcing you to tune both systems so that problems don't occurr.
RepetitiveYou'll find yourself repeating the same operations on WHMCS and WordPress just to make them look similar. For instance the first thing you're going to need is to produce two versions of your template. One that works for WHMCS and the other for WordPress. Making things twice surely isn't the most wise way to invest time. It's a counterintuitive process that makes you waste time daily.
Superficial integrationThere are plugins that act as a bridge between WHMCS and WordPress but this is not something that magically happens. The integration is superficial. A great part of it consists into sharing login session and using iframes or workarounds just to make visitors think that they're browsing the same website.
ConclusionI can understand why so many developers and companies put efforts into making WHMCS and WordPress as integrated as possible. In the short run it looks a great idea because we're getting the best from both platforms but let's look at the big-picture for a moment. Why can't we use WHMCS in place of WordPress?
It takes weeks to get a decent integration between WHMCS and WordPress and keeping it functional is a never ending process with all the cons I previously listed above.
Many seems to forget that WHMCS offers a lot of resources to expand functionalities (eg. Action Hooks and API). With them transforming WHMCS into a complete CMS like WordPress is absolutely possible and takes just few weeks more of work than completing a clumsy integration.
It took us about 2 months to develop Mercury, the module we use on our website for news, blog, Lab (a platform to request features, report bug and see/rate projects on which we are working), documentation and changelogs. It even supports sitemap, Open Graph Protocol, scheduled publish, SEO-friendly URL, a perfect implementation of canonical URLs and widgets for all tastes.
With Mercury we don't have to deal with two distinct systems. It is all part of WHMCS and there's no need to integrate anything. In the long run this solution is the best you can get. It will save you a lot of time, it's easy to manage and ideal for daily use.
Over the years for our customers we completed a lot of integrations of WHMCS with other CMS but now it's no longer needed. With Mercury we can get rid of the need to rely on third-party CMS.
Next time you start working on an integration, think twice. Use Mercury or code your own solution using the tools that WHMCS provides.