On the plus side, SiteGround offers free automatic daily backups, access to the Cloudflare CDN, high-performance SSDs for all plans, unlimited email accounts and integration of the free LetsEncrypt SSL certificate into sites. The company does limit bandwidth and storage, but even those who claim to offer so-called unlimited bandwidth and storage really have some limits in its terms of service.
Many web hosting services offer so-called unlimited or unmetered service for whatever amount of bandwidth, disk storage and sites you use. It's important to understand that most terms of service actually do limit the definition of "unlimited" to what's considered reasonable use. The bottom line is simple: if you're building a pretty basic website, unlimited means you don't need to worry. But if you're trying to do something excessive (or illegal, immoral or fattening), the fine print in the terms of service will trigger, and you'll either be asked to spend more or go elsewhere.