Do you release tension and let the weight drop on deadlift like webm related, or do you slowly control the eccentric...

Exactly this. During training there is no reason to pick up a weight you can't control. It barely does anything to make you stronger.
Competition form is a way to prove strength, but it isn't going to make you stronger.

Dropping the weight is safer, especially at near-maximal loads
It's also less effective for developing strength and muscle

youtube.com/watch?v=o1S091SiO8g

Advice from steroid users is completely worthless for natties. Try Richard Hawthorne
youtube.com/watch?v=Ffy3nCV61-o

That's a retarded take. To get better at one rep max you have to do one rep max. Exactly in that style, form and with the weight you will load in comp. I am not telling you to do that all the time, but you absolutely positively need to handle 100%+ loads in training, just like you need to handle 50%.

You only have to do this in the weeks leading up to competition to practice the form.
For actually making gains throughout the year, slow and controlled is superior

Control. It's annoying to slam when I'm doing a set to drop it as it tends to bounce/roll away. This is especially a problem now that I've switched to home gym with bumpers (I only have bumpers). I've done this so much that even if I'm doing just a 1RM I'll still control it down just because I'm used to it.

Dunno about all the stuff above about how much the eccentric will help gains in a deadlift. Sounds reasonable though.

Could have sent that guy right to snap city for life. If he'd have punched the dick kicker and kicker took a bad fall and died I'd make sure he got off Scott free or at least with a hung jury were I on it.

You have to do it throughout the year on all of your specific cycles if your goal is strength. Whether you do shot put, weightlifting or powerlifting, you will have multiple high intensity training cycles throughout a year. That is not to say eccentric is unimportant, but it isn't particullarly useful if your goal was to increase your deadlift.

If I increase my 3 rep max including eccentric to 500lbs, obviously my 1rm will be higher than that without ever touching a 1rm in training.

Almost everyone doesn't control the eccentric on deadlifts because of the danger and for muscle soreness because of the total body nature of deadlift. You can't compare the deadlift to something like the OHP or Bench, any simple misgroove in the deadlift can hurt you, if you want more hypertrophy based deadlift for hamstrings and glutes then do RDLs

>deadlift
>doesn't lift when the weight is dead

yeah that's a yikes from me

There's only danger because everyone is obsessed with chasing numbers during training cycles. Not focused enough on actually getting stronger in these positions.
If you use a proper weight you can control and put all your focus on perfect form then there is little risk. It's as safe as bench/OHP.

Yes it will, however if your goal was to increase your one rep max you would need to do as much maximal reps as your CNS would allow you. Which is not exactly many, but still. Eccentric affects the speed more then anything, hence, for example, it's a really good idea to do slow descent-quick ascent squats if your desire was to increase your clean.