On a personal note -- I'm an individual who HATES browser notifications -- I have them disabled GLOBALLY...
Browser notifications are a huge source of "unfiltered communications" from sites with questionable motives. There are legitimate sites that use them - but our experience with end users has shown that disabling them removes just another vector for click-bait scams and links to questionable sites. While this concept doesn't apply to the SmarterMail application on it's own - there is a whole wide internet many of us are fighting against to keep our users safe online.
It's understandable to ask why someone wants notifications off -- but the real question is if a user preference is chosen, why is the application persistently notifying about it? Once a user dismisses the warning, that should be the end of it. For me, if I'm in webmail, I'm notifying myself - or it has a title-bar change to indicate new mail.
(just a third-person opinion) --
MailEnable survivor / convert --