If you want to work in academic research you need one (unless you aim to be some sort of assistant forever).
If you think you’ll be in industry then it *might* help career progression, depending on what you’re doing. Don’t assume you’ll automatically get paid shedloads more because you have letters in front of your name. You do a PhD because you really want to spend another 3-4 years learning an enormous amount about an incredibly specific subject.
I’m very glad I did mine but when I finished I went into a graduate entry level job in industry and it’s quite possible I’d have seen the same career progression without the additional qualification. You need to figure out what you want from it and financial impact. For me, 3 years of MRC funding meant I could maintain a basic lifestyle without building up much more debt. Not sure I’d have done it if I didn’t get that funding, despite how much I enjoyed pushing my intellectual limits a bit.
Edit: should have signed that Dr Nice :wink: