In general Google treats subdomains as separate sites.We recently move blog to subdomain and here the issue we are getting
Disadvantage on subdomain
A subdomain works like a separate domain in terms of authority, you would have to spend more time and money for building the authority for your root domain compare to when the blog was under a /subdirectory/ or on /separate-pages/.
The strength of the root domain does not transfer to the subdomain. The existing authority of the domain does not affect the subdomain and you would be starting from scratch.
results in better root domain authority
You have to perform separate SEO activities for this sub-domain.
Subdomains are useful for audience segmentation as well.
Subdomain is an advantage if your main domain is already ranked well for your targeted keywords because your subdomain has a separate opportunity to rank and therefore give you a greater share of that valuable first page of Google real estate.
Advantage of subdomain
The advantage of having sub-domain is that you can target specific audiences with specific sub-domains.
File system and database are separate from main website
If you are planning to follow a corporation structure with multiple sub-enities under one umbrella, subdomains work for you.
If for any reason, your sub-domain is penalized, you won’t get any problem to your main site.