The alliance could be crucial. Cruise is increasingly focusing its attention on autonomy as a service with projects like its electric shuttle Origin, and these will rely heavily on the cloud to connect with each other and with passengers. Money, meanwhile, could help Cruise weather the pandemic and better compete with his rivals. like Waymo.
It is not as vital for Microsoft. However, this gives the company a foothold in driverless transportation as well as a prominent customer. This could easily justify the expense for both prestige and exclude Google and other competitors.