I think the best thing about being pro is the confidence you feel when somebody from a publisher or a big company says "yes, your work has been approved to go in this book/game/product". I was absolutely over the moon when I did some work promoting Dragon Quest IX and they had to send my portfolio to Square-Enix and one of my fave games publishers gave me the thumbs up like "yes, you're good enough". Same for when I worked on "Doctor Who: The Women Who Lived" and sending the work to get approved by the BBC, I was nervous every single time and elated when they came back approved and a bunch of my pieces got into this big shiny book and we did a signing at Forbidden Planet and things, and the local paper from my little town in the middle of nowhere interviewed me, hahaha.
Worst things though... When you're working as a pro, you're almost certainly working on other people's IP, and you'll probably end up with no time to draw anything for your own enjoyment or to make comics of your own, and if you do, you'll probably feel guilty. The money isn't amazing for how utterly life-consuming it can be and... oh god, don't get me started on chasing up late payment on your invoices.
There's also a lot of... sexism...classism...racism... in publishing that's kind of a nightmare. It's hilarious now that the print publishers all complain now about how their sales are falling while webcomics are booming and it's like well duh, you guys turned down all these talented young women and focused on an ageing audience so those women all went online to make their content that's relevant to a huge untapped audience thirsty for content on these new online platforms, what did you think was gonna happen?
Right now, I'm pretty happy doing a creative, but not entirely illustration-focused job a few days a week to pay my rent while finally for the first time in years being able to make an original comic. When I was a full-time pro, that would have been impossible. I was stressed, barely able to afford to live and had no creative energy for any original work of my own.