I've used source controls for a few years (if you count the Source Safe years), but am by no means an expert. We currently are using an older version of Sourcegear Vault. Our team currently uses a check out and lock model. I would rather switch to a update and merge model, but need to convince the other developers.
The reason the developers (not me) set up to work as check out and lock was due to renegade files. Our company works with a consulting firm to do much of our development work. Some years ago, long before my time here, they had the source control set up for update and merge. The consultants went to check in, but encountered a merge error. They then chose to work in a disconnected mode for months. When it was finally time to test the project, bugs galore appeared and it was discovered that the code bases were dramatically different. Weeks of work ended up having to be redone. So they went to check out and lock as the solution.
I don't like check out and lock, because it makes it very difficult for 2 or more people to work in the same project at the same time. Whenever you add a new file of any type or change a file's name, source control checks out the .csproj file. That prevents any other developers from adding/renaming files.
I considered making just the .csproj file as mergable, but the Sourcegear site says that this is a bad idea, because csproj is IDE auto-generated and that you cannot guarantee that two different VS generated files will produce the same code.
My friend (the other developer) tells me that the solution is to immediately check in your project. To me, the problem with this is that I may have a local copy that won't build and it could take time to get a build. It could be hours before I get the build working, which means that during that time, no one else would be able to create and rename files.
I counter that the correct solution is to switch to a mergable model. My answer to the "renegade files" issue is that it was an issue of poor programmer discipline and that you shouldn't use a weaker programmer choice as a fix for poor discipline; instead you should take action to fix the lack of programmer discipline.
So who's right? Is check in - check out a legitimate answer to the renegade file issue? Or does the .csproj issue far too big of a hassle for multiple developers? Or is Sourcegear wrong and that it should be ok to set the csproj file to update and merge?
The problem with update and merge that you guys ran into was rooted in a lack of communication between your group and the consulting group, and a lack of communication from the consulting group to your group as to what the problem was, and not necessarily a problem with the version control method itself. Ideally, the communication problem would need to be resolved first.
I think your technical analysis of the differences between the two version control methodologies is sound, and I agree that update/merge is better. But I think the real problem is in the communication to the people in your group(s), and how that becomes apparent in the use of version control, and whether the people in the groups are onboard/comfortable with the version control process you've selected. Note that as I say this, my own group at work is struggling through the exact same thing, only with Agile/SCRUM instead of VC. It's painful, it's annoying, it's frustrating, but the trick (I think) is in identifying the root problem and fixing it.
I think the solution here is in making sure that (whatever VC method is chosen) is communicated well to everyone, and that's the complicated part - you have to get not just your team on board with a particular VC technique, but also the consulting team. If someone on the consulting team isn't sure of how to perform a merge operation, well, try to train them. The key is to keep the communication open and clear so that problems can be resolved when they appear.