I do think that each project should have his own repository. Imagine that you're a developer working on the project X, and someone ask you to revise a PR in the project Y. In order to run the test suit of Y in your machine, you need to drop everything that you're working on the project X and switch your current branch.
Also, there is one point much more important: git history. If you have one repo for all projects, you will have a giant history and it may be harder to navigate in the history.
About squashing, I personally prefer not to use it. Merges is my preferred way to go, but I do no see any problems of squashing changes instead of merge.
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I do think that each project should have his own repository. Imagine that you're a developer working on the project X, and someone ask you to revise a PR in the project Y. In order to run the test suit of Y in your machine, you need to drop everything that you're working on the project X and switch your current branch.
Also, there is one point much more important: git history. If you have one repo for all projects, you will have a giant history and it may be harder to navigate in the history.
About squashing, I personally prefer not to use it. Merges is my preferred way to go, but I do no see any problems of squashing changes instead of merge.