Pros and cons of providing beer and wine

I definitely wouldn't leave this until the day of the wedding. Wine keeps well if you store it correctly! I'm sure the bartender could give you an idea of how much to buy, but there are some states and liquor stores that will let you return unopened bottles. I would also research where you can get case discounts (usually 10-20%). You could also see if you could store it at the venue prior to your date so you wouldn't have to worry about transporting it day-of.

I've been thinking of this myself. Here's where I'm at
You absolutely need event insurance either way. Even with an insured bartender, it means multiple vendors. Did guest get sick off food or improperly refridgerated garnish? If you carry liability as well your party will be cared for while the insurance companies hash it out. Plus, it's not terribly expensive.
There's no time for anyone to run out and purchase day of but you don't want boxes sitting in a hot garage for weeks on end. Do you have appropriate storage?
If your thinking self-serve (which isn't the insurance problem people will say it is) how will you work that? Iced beers and sodas are relatively easy, but what about the wine? If it's left on tables will the catering staff replace empties? Is a champagne toast possible? How will you work soft drinks? Cans? Bottles? Glasses look best, but how will you make that happen?
I'm lost too, but I feel better knowing what questions to ask.

Doing anything other than getting ready for your wedding on the day of your wedding is a terrible idea. You can definitely get it yourself if you have a licensed bartender serving for you, but do it a couple weeks before, not the week of, and certainly not the day of! You'll have so many other things to worry about those last few days leading up to it. Getting your alcohol should not be one of them.

We are bringing our own alcohol and Specs - the local liquor store chain does free delivery to our venue.

Does your venue work with any liquor stores? Maybe you can see if you can find a store that will do this for a small fee?

We ordered our alcohol from Bevmo, it was nice because they delivered day of the wedding and took back unopened alcohol after. We did have an issue with our local BEVMO not sending the correct wine but no one noticed.

And I agree with a previous poster you will NOT have time the day of your wedding.to do anything except get ready. Whatever solution you chose take that into consideration.

I have no advice on this topic but I did want to share that Costco will take returns on any unopened alcohol, which is nice if you over buy. You’d probably have to double check yours, but the one near us does.