Because all my ram is already consumed. I have a 16gb MacBook running only a browser, vscode, ms teams, and the docker containers for the app and I have no memory left so I see a spinning ball every time I change windows. Ms teams was the final straw. Slack was about 300mb but teams is now 700mb+
Once you exceed it some of the content will go to swap, which is going to slow down the system (and wear an ssd faster). 400MB is not that much though, for me Code usually takes at least 1.5GB RAM.