I've been using TACC 99% of my freeway driving... and probably 50% of around town driving. It reduces the stress from driving IMMENSELY. I wouldn't buy a Tesla without it before... and especially since AutoPilot is now live with the 7.0 update !!!
Having used it for about 30 miles of driving today I can say that I will use it a lot. It is really easy to engage and to adjust speed. I generally don't like cruise or anything like that because I fancy myself an engaged and competent driver, but this is really fun. It's a new aid for the drive. You can engage it for a few miles, let the car do the work and then take over (or not). It's simple and intuitive. I have to say it was worth the wait. Very cool to get the feeling of a brand new car experience OTA. Kudos Tesla.
The TACC is super nice for the kind of driving I do (bad commute traffic where the speed fluctuates between 0 and 60 mph). It is great not having to keep stopping and starting all the time. I just got the 7.0 update but have only had a chance to try it briefly so far. I suspect it will also make my commute nicer, once I get used to it.
And don't forget the auto dimming high beams! Those are a major benefit when driving on the dark and windy road my house is on.
I use TACC all the time on pretty much any trip requiring more than a few miles on the freeway.
In some ways it's kinda like a buddy system. It looks after me, and I look after it. For the first month or so of ownership I was extremely cautious with it and had my foot hovering over the brake all the time.
Now with V7 I'm really nervous with the lane-steering where I have my hands near/on the steering wheel ready to take over and I've been taking over when it's even slightly off.
It's probably going to require a couple months for me to get used to it, and for all the data from the drivers to improve the system.
I am salivating at the idea of it with the Model 3. I hatttteeee freeway driving but am forced to do it regularly. I TRY and use cruise control but the other drivers on the road have other plans for me so I am constantly engaging it, braking, resetting, etc... Even just having TACC would be a huge bonus for me, much less auto lane steering.
I'v used it around town and on a short highway trip and it worked freakishly well! There are things it trys to do like follow a car through a sharp turn (in the city low speeds) then gives up half way through and alarms so you have to be careful in situations like that.