Hosting a subdomain with Blogger is your choice. But if you want more clarity, it can be used in case your main site is focused on services and products. If your main domain is used for business website or an ecommerce site or service site. In such case you may need to write some Blogs or Articles related to your services and products. In that case managing Blogs and an ecommerce or service site in the same place and diretory may create confusion. Therefore, to make Blogs easily manageable you may need to host a subdomain with Blogger.