Is a doc necessary?

I believe it would still be beneficial. Check out their duties and see if it's still something you would consider.

https://www.hollowhilleventcenter.com/wp-content/uploads/2015/11/RESPONSIBILITIES-OF-DAY-OF-COORDINATOR.pdf

I wish I could have afforded one. It would have taken away a ton of stress and things would have gone more smoothly.

Most DOC's do a bit more than that. They're also in charge of confirming the wedding date with vendors (to make sure they're going to show up!), developing your timeline, sending people down the aisle, having a rain plan, etc.
I'd shop around and focus on planners who do "month of" coordination rather than breezing in on the day of

So, I’ll say one is not “necessary” but I’d highly recommend one! Our day moved so smoothly thanks to our DOC! She assisted in set up, helped move our ceremony along perfectly, as well as our cocktail our, dinner, and reception. I also feel like she worked seamlessly with our DJ, which really helped out.

I won't be having a DOC for a few reasons:

1) I am a super planner and will be setting everything up the morning of the wedding with the help of my bridal party, parents, and some family members

2) I've hear horror stories about how the DOC, because you don't know each other well, doesn't know your exact vision so when making decisions, the bride ended up hating what they did

2) My best friend/one of my matrons of honor used to be an event planner so she will be a huge asset and act as my DOC because I completely trust her

Yes.

You might not want that expense but let me tell you: You do NOT want to worry if everything is set up right, people are where they need to be, vendors are there and doing what they should be.... etc. etc...

If you are going to get one, read reviews. I've heard some horror stories. Also, depending on the wedding size, I'd say you could go both ways. Our wedding is small so an extra 2-3k sounds silly to us considering we can handle confirmation calls and aid in set up if necessary. A bigger wedding, I'd probably look into it.