When does SD-WAN actually become worth it for a small multi-site business?

For companies with maybe 3 to 10 locations, where do you think SD-WAN starts making sense over a more traditional setup? Assume they rely mostly on cloud apps and VoIP, have dual internet connections at some sites, and do not run much infrastructure in a private data center. Is the main benefit better failover and centralized management, or does the value only really show up once the network gets larger?