Disadvantages of Subdomain

1. Separate SEO Efforts: We have to develop and implement separate SEO strategies for each subdomain. 
2. Link Building: When we create a new subdomain, we have to build high-quality backlinks for that subdomain from scratch.
3. Maintenance Complexity: Managing multiple subdomains can increase the complexity of website maintenance, requiring separate hosting, SSL certificates, and server configurations for each subdomain.
4. SSL Certificate : Each subdomain often requires its SSL certificate, which can be both costly and burden to manage, especially for websites with many subdomains.
5. Cost : Hosting multiple subdomains lead to additional hosting costs, depending on the hosting provider's pricing structure.
6. Branding and Trust : Users may trust the main domain more than subdomains, potentially affecting credibility and branding efforts.
7. DNS Lookup Overhead : When a user visits a subdomain, their browser needs to perform an additional DNS lookup to resolve the subdomain to its IP address. This can add latency to the page load time, especially if the DNS resolution is slow.
8. Cookie Isolation : By default, cookies are often scoped to the full domain, including all its subdomains.