Your suite takes ninety minutes on one machine. You need to test Safari, and your team is on Windows. Both problems have the same answer.
Grid runs your tests on other machines. Your test code stays where it is and sends its commands to a Grid, which passes them to a browser somewhere else. Because everything already travels over the WebDriver protocol, sending it to another machine changes almost nothing in your code.
Two parts:
The Hub receives requests and decides where each one goes.
Nodes are machines that actually run browsers. A Windows node with Edge, a Mac node with Safari, several Linux nodes with Chrome.