Blog comments and replies can be used to generate community and conversation on your website. This is an effective way to engage with potential clients and begin building a relationship with them. It also allows for you to open dialogue and answer questions that people considering your services may have. This relationship is the first step in building a reliable client base.
However, be aware that the level of interaction on therapy blogs are much lower than on normal blogs, like cooking or craft blogs, because generally people do not want to publicly post about mental health. This is why most therapists decide to forgo blog comments as moderating spam is not worth the little engagement that you can expect.
Stick to generating a following on social media. This way you can still create a community and begin discussions with those who are willing to converse publicly without having to deal with the headaches of spam.