Hi, I did this, I worked for publishers in-house for ten years, then I made the switch to freelance about ten years ago and did it for five years - I've since made a big career change into something different.
Pros
Being freelance meant I could choose my own hours, within reason, which suited me much better than standard office hours.
Also meant I could work from anywhere, not just from home, which suited my life at the time.
I was able to branch out into related/different areas, more than if I'd been restricted by employment.
Cons
Your reputation is at the whim of any person who gives you a freelance job. You could edit an entire book manuscript amazingly, but get feedback such as "I would have added a comma to this one sentence". Learn to accept constructive criticism but to let the annoying comments wash over you.
Rate of pay is not amazing - publishing companies tend to have set (low) rates. Much better to tout yourself to individuals, self-publishing authors for example, to set your own rate, but even then the pay is not amazing. Where you live and whether there is another income in your household makes a difference.
No sick pay, holiday pay, pension contributions, training.
Tips
As you are already working in the field, gather all of the contacts possible, then when you become freelance really use your connections to network and promote yourself.
Every work interaction is a potential new client/job. For example, I was working in the academic publishing field. If a publisher asked me to edit a text book manuscript with multiple authors who I would need to contact with questions, each of those authors was a potential new client, and often did become one. So manage your communication well.
Have a work email address and a work bank account.
Give some thought to when you will work, how many hours you will work, and how you will structure your time, allowing enough time to complete the work but also for admin - replying to emails, looking for projects, invoicing, etc.
Get set up with tax self-assessment well in advance. You don't want to be setting this up in a rush as the deadline approaches! It worked best for me to operate as a "sole trader" and complete a self-assessment tax return, but your circumstances may be different.
I'm very happy to answer any questions or give more advice if you want!