I do see value in occasionally pushing up against my comfort zones. Not in a punishing way, like enduring all manner of shit because it's supposedly good for me, but rather like a periodic testing to see if the parameters of my comfort zones have shifted, expanded, or contracted.
I mean, there are a lot of foods and condiments I like now that I told myself I hated as a kid without even trying them. If I hadn't ever chosen to bump up against my self-imposed limits, and to actually try these things, I wouldn't be enjoying yogurt, coffee, mustard, and some other things as much as I am today (yes, these are all foods that I never even tasted until I was an adult). I still wrestle with feeling awkward around people, especially in group settings or parties, and so I push my comfort zone a lot to get past that because I do want people in my life and to be more at ease in groups without needing alcohol, so I am willing to look foolish and feel uncomfortable to achieve that goal. But if I ain't feeling the need to go there, I guiltlessly stay home and enjoy my comfort zone.
I approach the boundary-testing of my comfort zones as an exercise that I do solely for my own benefit, if and when I see fit to do so. If I find that I like my comfort zones just as they are and have no need to push past them anymore, that's perfectly fine, too. But while I do think that it is beneficial to at least look at our comfort zones and occasionally test them, I don't think anyone else should be telling me which comfort zones I should give up or test - and I hope I haven't come off as someone who tells others what zones to test, although I know I've made suggestions to people as ideas to look at and see if it rings true for themselves.