Shared is cheapest but has limits. Knowing when to upgrade matters.
1. Slow speed
Dozens of sites on one server. PageSpeed drops.
2. Resource limits
CPU, RAM capped. Traffic spike — 'Resource Limit Reached'.
3. Security risk
One hacked neighbor — all at risk. Shared IP — neighbor's spam affects your email delivery.
4. Plugin/software limits
Custom PHP, Node.js often unavailable.
Upgrade signs
Site 3+ sec, 1000+ visitors/day, e-commerce.