Classic question: "What does a compressor do and why do you 'need' one?"
A compressor does 1 thing: Reduces dynamic range.
Depending on how and when you apply that dynamic range reduction can do many different things, many of those opposites (but not at the same time): Add punch OR add sustain; thicken the sound; flatten the sound; even out level differences; tame loud transients; emphasize weak transients; hide sloppy playing; emphasize sloppy playing; it could be transparent; it could 'sound compressed'; etc. etc.
And it's a non-linear processing effect. It's not a 1-to-1 relation. With distortion, it's 1-to-1. Regardless of what signal you put in, if you turn up the distortion knob, it distorts more. With EQ, if you turn up the 600Hz band, you get more of that band. Compressors are reactive and do different things not only with different settings, but depending on what the sound is like coming into the box.
So the best way i answer the question is, you don't 'need' one unless there's a specific character lacking in your uncompressed signal that a compressor will address.
I use compression all the time when producing/engineering. I also spent 1992 through 2023
without a compressor for my bass rig, other than, some of my amps had built-in compressors that were basically on/off/no other settings. If i was recording, i didn't want baked-in compression. I wanted to address that as needed when editing and mixing.
You don't NEED-need a compressor. Is it a handy tool to have in your arsenal if you know how and when to use it? Yes. But it's often misunderstood, misused, and abused. Especially because a well set-up compressor you don't "hear" until you turn it off. And there's at least as much bad information on the internet about compressors as good info.
Check out
this post.
And
this post.
And also
this post.