It's a relatively simple version control system so it works great for an individual or small team (less than 10 people). But if you have a medium to large team, especially one with members distributed over a large geographic area, or one where individuals need to be able to work "offline" without access to a central server, Apache Subversion will likely not be the best choice.
Also, if you're maintaining an open-source project where outside people will be interacting with your code repository, git is probably a better choice because it's becoming the de-facto standard these days and what most developers are familiar with.
Serena CM is well suited to highly controlled, audited, and process driven environments. It will allow strict segregation of duties, and change traceability. If implemented correctly it will help you quickly build trusts with your auditors. It is also well suited to environments that require constant branching and merging. Due to the complexity of the product and learning curve for your development and operations team it may be overkill in a small shop with loose rules
Code Promotion: Dimensions CM allows supervisors to control changes to code, in that they delegate requests to developers, and act as a gatekeeper prior to promoting to the next environment. This functionality is configurable so you can set up a workflow that best fits the structure and requirements of your own company.
Code Repository for changes and versioning: Code can be checked out by item or by synchronizing folders. Code revisions can be compared against other revisions or work files. Item histories show which developers made which modifications, and which supervisor and operations personnel were involved in assigning the request and promoting the code to each environment. Additionally a pedigree will show a stream diagram which graphically displays branches and merges.
Deployment: Serena Change Management offers help automating deployment including integrations with SVN and Jenkins. Its newer versions also have a powerful graphical deployment automation tool (Serena Deployment Automation- SDA). It comes with a certain amount of licenses built-in. If you have a many nodes to deploy to there will be separate licensing costs for that.
Distributed development - I've never worked in an environment where distributed development (developers widely scattered geographically) was a factor, but that's why git exists.
Merging - Merging of code from one branch to another can be painful, especially if it's not done frequently. (On the other hand, doing merges is one of the reasons I get a nice salary, so I can't complain too much!)
Acceptance - Let's face it, git is what "all the cool kids are using." If you've got a bunch of developers fresh out of school, they'll probably know git and not Subversion.
The only major negative that I have encountered with Serena CM product is that the very power and flexibility of the tool means there is a risk that you will make a mess of things. In other words it gives you plenty of rope to tangle yourself with. I recommend careful, well thought out deployments implementing the built in roles and workflows that can be turned on and configured, using a consistent methodology.
My experience with the Serena help desk support has not been impressive. Though reasonably polite and diligent, the technicians were well trained, and often gave bad advise and terrible scripts. On several occasions I had to rewrite scripts they have me; if I had run them as provided they would have caused even more difficulties than the problem I was trying to solve. I speak of the support in the past tense because I conditioned myself not to call them, it was usually just easier to solve nay problems my self. They do have a good account management team though, and for any major issues you can go thru them.
While there are interesting alternatives, such a GIT, Subversion has been a breath of fresh air compared to its predecessors like CVS or Microsoft Source Safe (now called Team Foundation Server). Its ease of use and high adoption rate is going to keep me using this product for years to come.
Git has become the new standard of version control, with its support for distributed design. As a tool to manage and control versions, Subversion does it well, but Git is the future.
Serena CM is superior to Microsoft Team Foundation Server (TFS) in overall functionality, but does not have very good native integration with Microsoft. Therefore in a Microsoft centric shop with no audit needs ,TFS would be better. Otherwise I would choose Serena CM
Serena has facilitated our annual completion of various audit and technology control certifications. These certifications make a huge difference to our company's reputation and bottom line.