Subdomain is a sub from main domain, and many businesses do not like to use subdomains because they feel a subdomain give disadvantages in many ways, e.g. being ignored by bots and index spiders in search engine (SE). Fell look less professional if compare use main domain and so on.

Actually subdomain does not matter if you use it, which is important how you choose the right keywords that many people search with few rivals, and can optimize those keywords using search engines optimization maximally. If you can do it then no problem you use your subdomain, because SE spiders and bots will still index and give traffic to your subdomain

You can make each subdomain as a separate category if you have to submit to search engines, by doing this you still get a subdomain with good rankings for each subdomain will be seen by SEs as a new website with the homepage or the index itself. You can also try to create subfolders on subdomains so that SEs can interpret the folder as a set of site information.

If the primary domain backlist affected then this will affect the subdomain, because the subdomain is considered a part of the primary domain name, there are a number of people who feel worry about this issue where they are banned subdomain due to harms with the primary domain name, such in adult content web site own violated certain agreements that they’ve signed with service providers that don’t require a domain that is utilised for adult material, but when used correctly in domain name and does not violate the existing rules, then you are supposed to not worry when you would like to usage a subdomain.

Therefore there is no problem to use a subdomain If you would like to build up every subdomain as a separate identity from a website, but if you do not want to use a subdomain, then you can use a domain name by using a certified landing page