It’s quite rare for any site to have a ton of email-only participation. 25 years later, people are pretty darn comfortable with the concept of a web browser 
The reality is that email replies capture a small percent of the time people are “on the go” and want to reply but all they have access to is email. It is a convenience feature.
If you turn it off, you turn off convenience – but it’s not essential to survival in my experience. I’d still recommend it though.