I use Mail.app with Gmail and an elaborate set of filters/folders - Why should I use this product? - I consider Mail.app (and to an extent Thunderbird - or for

I use Mail.app with Gmail and an elaborate set of filters/folders - Why should I use this product? - I consider Mail.app (and to an extent Thunderbird - or for that matter Alpine) adequate for my emailing needs - what feature do you have that I didn't know I needed but wont be able to live without?