If you modify/comment an issue or a wiki page..., and want to know if someone responds to your comments, you have only one possibility: 'watch' this issue and redmine send you modification notifications by e-mail (if the option is set).

It could be interesting to have another suscribtion option: resuming this modifications into a dedicated page ('monitoring') or insert it into the Activity page.
Another option could be to add a widget to insert this information in 'My Page'.

I think the interest is to use one and only one tool to manage your (or others) projects: Redmine, without the need to check your mailbox.