I know there are lots of answers both here (e.g. this and this) and elsewhere which deal with subdomains and their impact on SEO. However, often the questioners are either asking about subdomain versus subdirectories, or they have an existing well trafficked main domain and are asking how introducing a subdomain will impact their existing site.
Our question is simpler than that.
If we are starting a website from scratch today, and we're worried about ranking well in SERPs for two keywords xxx and yyy, is there any disadvantage to using a subdomain as in:
xxx.yyy.com
versus
xxxyyy.com