The advantages are many if you have a good pool of technical knowledge to draw from including skills like Javascript, SQL, Java based application support, HTML and CSS with knowledge of require.js, protovis, D3, etc. The biggest advantage is that the platform is largely opensource and you can customize the outputs to work the way your business does. When we subscribed, there was not user limitation, which is pretty nice. Generally if there is a JDBC connector for a datasource, you can get data into the platform and work with it well. Later in my life I discovered CDATA's JDBC drivers that reach out to a lot of the REST API based SaaS offerings out there and let you use regular SQL statements against them, which is really nice. Pentaho Data Integration has a lot of great orchestration and connectivity features lacking in other products. I like that the suite's products save files either as zipped up XML files or XML files with a different extension. That makes tracking and managing changes easier.
The disadvantages are the flip side of the flexibility and knowledge requirement. The enterprise edition has become a bit easier to manage from an upgrade standpoint than it used to be. If you use PowerBI or Tableau, you can get to pretty very fast, but you are largely locked and committed to their way of doing things and tool updates. Pentaho is a bit harder to develop content for, but you have complete control over how it is shown and interacted with. No nickle and dime games with turning features on and off or trying to share content with other users. On the other hand, licensing the suite is like a big whale of a payment.