If you have Meshes are Assets enabled in ProBuilder's preferences, Unity seems to constantly thrash the Asset Database whenever you interact with a ProBuilder object. The worst case for this seems to be when you attempt to drag-select multiple objects in the Scene view, which can hang the editor for 30+ seconds and generate hundreds of megabytes of garbage. Here's a screenshot of what the profiler looks like when triggering one of these spikes: https://imgur.com/a/Ombo9Cr Meshes are Assets is a very important setting for our team, since it allows us to keep the scene files small and diffable in Git, while letting us store the binary mesh asset data in separate LFS files. However, using Meshes are Assets is currently causing our workflow to be unusably slow for our level designers due to this behavior. I have filed a bug on the issue against Unity 2018.1.5, but I have also verified that it still reproes on 2018.2.8.