Cloud *aaS is best suited to several major use-cases:
0. Experimental projects of limited duration
1. "Peaking" overflow capacity for burst of transactions or daily sinus maximum load (/.-resistance)
2. Batch jobs (ephemeral computing)
3. Disaster Recovery/Business Continuity (DR/BCP)
4. Informal IT to bypass bureaucracy
Source: Hi, I'm a former client-facing Fortune 200 AWS consultant from back in the day. I don't own Amazon stock or have any current conflicts-of-interest.