This mantra is very important to me and something that I'm super glad to have heard right when I was getting started in webcomics a few years back. I do worry at times about "rushing" too much and producing somewhat sloppy work at times... But it's always reassuring to see beta readers not even notice many of those little mistakes/weirdness on a first pass or even until I mention it afterwards.
This basically sums up my feelings exactly:
Like, I still have a lot of learning and improvement to do as an artist, so I find even when I do spend way more time on particular panels or whatever... the results aren't usually drastically better enough to warrant the extra time spent. And by continuing to push out a lot of work quickly (aka, practice) I notice my skills continuing to improve at a pretty acceptable rate anyways so... it's a win-win, I guess. "Better at being faster, and faster at being better", I love that!
Lastly, definitely agree with others in the thread though about trying to find a good balance and not being too complacent / cutting too many corners. All good things in moderation, y'know? You still want the end product to look good, even if not completely amazing, and it's good to think from time to time about which corners you're cutting and why. My rule of thumb is that any shortcuts I take should either only drop the visual quality very little, or be on par with what I was doing before, but faster, and should preferably improve the overall presentation as well.
For example I've recently started using the marquee and path tools to generate my speech bubbles where I used to hand draw them before. At worst it's a side-grade, but at best it gives me neater, more consistent and easily editable bubbles than what i had before. Another one is my shading- I've been trying to simplify it a bit recently. At worst, it's less detailed, at best it actually removes some visual clutter and saves time on tiny details that were barely noticeable when zoomed out at regular reading size.