When someone comments on your Page updates, you get a notification in your Facebook Page’s admin panel and on your iPhone (if you use Facebook Page Manager).
It might be easy to simply like their comments and then be on your way.
But replying will actually create more reach and engagement. Here’s why:
When you like their comment, they get a notification on Facebook (and sometimes by email) saying “Name of Page liked your comment”. There’s no reason for the user to revisit the update because they’ve gotten all the information they need.
When you reply to their comment, they also get a notification on Facebook. But in order to read your comment, the user has to return to the update. This increases more reach and engagement simply because the user is pulled back into the conversation.