Apart from in my very earliest days here, when my attitude was perhaps characterised by a degree of arrogance, I have (I think) responded to every comment I've received. As others have said: it's only good manners, it requires little effort, it can open up interesting conversations/connections, and (as beth says) it is more likely than not to attract that reader to read more of one's efforts. I believe my responsiveness has definitely played a part in how generously readers have continued to comment.
However, it is also true that a largish majority of the comments I get, (and perhaps you too?), come from fellow authors (

Hi, folks! And thanks!) who know first hand how important the feedback is to one's motivation to write more - especially perhaps in the earlier days of our writing careers. Many of our more experienced colleagues, I know, have transcended this vanity, or insecurity, and are motivated to write solely by the pleasure of the act itself. Maybe one day ... !
