OK I'm going to answer this in a couple of episodes because its late here and Harvest is a big topic.
Firstly CA Harvest (which is what version 7 of the product is called, version 5 is CCC which I cant recall the expansion, version 12 is called CA SCM) is a lot more than just a SCM tool - in the same way ClearCase is a lot more than an SCM tool. SVN, CVS, git, hg are all base-standard SCM and little more.
What you get with Harvest is SCM + Policy. It gives you a place to store and version your code and wrap it all in a policy of how that code matures though your organization from dev to prod. Do you have a policy in your organization that a Lead Developer needs to sign off on the code before its released to QA ? Harvest allows you define the signoff as a policy, and enforces it - you cant migrate the code from the "Dev" state to the "QA" state until one of the people in the project designated as a Lead Dev does exactly that. Do you have a policy that any SQL code needs signoff by a DBA before it progresses ? Harvest allows you to define that policy, and enforces it - so you might need both Lead Dev and DBA signoff before code migrates.
Harvest is by no means a tool for most software organizations - it is typically used in the finance industry, or in business' where a very strong regulatory framework governs what they can do. Banks need to comply with Sarbannes-Oxley, which has very strong auditing requirements. Harvest provides the ability to define all kinds of controls and process around how changes to the Banks assets move through their lifecycle. I know large public transport organizations that are responsible for the safety and punctuality of millions of people every day, that need the tightly defined control mechanisms that a tool like Harvest provides. I also have seen Harvest used in environments where 1000's of developers use it everyday - yes, I'm not exaggerating, literally 1000's of devs in one organization, writing code for a worldwide retailer, pushing IT solutions out their door everyday to the stores around the world.
Harvest is not perfect, thought version 12 is much better. It has too many "that's just stupid"-moments, it does per-file versioning ala CVS, and CVS-like branching and directory versioning (or lack thereof), with all the fun we've come to know and fear. Once you know it and accept it though, its isn't inherently slower than any other SCM I've used. It just has a bigger job to do than just version your code.
Another big win, and its even bigger with version 12, is its integration with other CA tool (and ability to integrate with non-CA tools, but not many at the moment) - defect tracking with Quality Centre, trouble ticketing with Unicentre Service Desk, software deployment to the desktop with SDM. You can define bridges between these apps that result in a lot tighter integration of these concerns, with the usually positive effects on accuracy and timeliness.
If your dealing with getting software out to a worldwide enterprise, with thousands of desktops and servers, mainfame/midrange/middleware systems, iron-clad change control processes, complexity, regulations, contracts, auditors, just a whole bunch of complexity, Harvest is just one tool in a whole suite of tools your going to need. If you just want a simple SCM for a team of 10 devs supporting a few hundred customers, its not a great way to go.
I'll try to add something about how Harvest actually works next time - repositories, projects, views, packages, forms, processes etc. That might help explain why some organizations use it, and why its not for everyone.
