If you buy from inventory you usually get the car sooner, but you can also get a great deal (a new car, I am not talking about Demo vehicles that are clearly tagged on the inventory page). Tesla's pricing algorithm for the inventory is very interesting and seem strange. Sometimes I see the exact same configuration on the page with two different prices ($500 to $1000 difference) - it looks like this is also driven based on pick up location and the supply/demand at that specific location. I live in the SF Bay Area and there are several delivery centers within 40 miles range - so I had flexibility. I ordered/configured my MY from the website, but then I checked the Tesla app multiple time per day for "early delivery" (inventory). After two days, I saw my exact configuration at Fremont for $1000 off. Since I had a referral code ($500 off) I was not sure if that works together. I contacted the advisor, who responded YES, both the inventory discount and the referral discount are valid together. Of course, by then the car was gone. So I checked the following days until I got my configuration at $500 off (plus $500 referral).
So, it is worth checking the inventory multiple times to get a really good deal. More difficult on a Y (higher demand), but I saw a Model 3 RWD at $4000 off the other day (see photo) and a 3 Performance at $5,500 off. It might be different in other locations/states - I can only speak for SF Bay Area.