Yes. Adding volume is always useful as long as you can still nail your other workouts.
@Mylobearpup, I moved your post under an existing thread that covers the topic in depth.
I find them useful in my triathlon training to add to my overall volume while not blowing up my legs between other key workouts. You can try some of the variants like Pettit+1 that have a couple sprints built in for a little extra something-something without adding much extra stress too.
As Mikael Eriksson posted above, two hours of Z2 per week is an extra 100 hours per year of training. That can be significant in the big picture.
Because of covid and my child doing virtual school, I’ve done almost all Z2, one hour at a time, since the fall. I’ve only been able to get outside to ride once or occasionally twice a week. I like to ride 7 days per week if I can and I feel that those 5-6 hours of Z2 week in and week out have maintained my fitness pretty well.
Prior to this I was able to ride outside a lot and often get a 2.5 or 3 hour ride in. I miss those but I don’t have much choice. My fitness is good though and I wouldn’t hesitate to go out for a 3 hour ride today given the opportunity.
I just started a threshold block (extending TTE right now) and I feel well prepared for it after all this Z2.
I’ve been slowly progressing my cycling volume since the pools closed. I got from 10 hours to regular 18-20 hours a week now and I’m planning to end it in the 20-25hours/week range. I also run for 3-5 hours a week, depending on the week, but don’t swim (as mentioned, pools closed).
I did this just by adding workouts in the afternoon, after work. I tried running and cycling, but running seems too stressful, so I just started doing 30-45 minute long easy rides, Z1. I’m now doing 45-60-minute Z1 rides and progressing them into low Z2 rides.
As far as I understand, volume is king, and if you can’t do 6 hours straight day to day as the pro riders do, it’s still better to do something to add extra stimulus than to do nothing (as long as you can sustain it).
Wow, I still dont get how so many of you are able to squeeze such an amount of workout hours in your day to day schedule which must also consist of job, family, kids etc. wow, just wow.
I am happy to get to 10h and even that asks quite a lot of juggling from me, my wife and my schedule.
People that can ride 20 hours a week probably don’t have kids! Or a wife!
Honestly, I don’t even enjoy riding that much week in and week out. That means a lot of long rides by yourself and I get bored doing that. One advantage of pro riders living in places like Girona is that they always have someone to ride with if they want.
The last couple of years before covid19, I had the opportunity to ride as much as I wanted. I couldn’t even find a partner with the same M-F free time to go on epic rides.
You also need the recovery time for all those big rides. A 3-4-5 hour ride requires a lot of couch time and probably a nap. 
May want to put n=1 here. I know multiple married guys with kids that are up at 4am and we enjoy it quite a bit.
Hats off to those that can do 20 hours per week on a trainer at 4am!
I only know one person who does 20h/wk, otherwise 12h is pretty much the limit. Pre-covid I used to commute ~45k each way 2-3 times a week. The other guys I knew doing 12h weeks year round were also long distance commuters. It’s the only way to fit it in and maintain healthy relationships, etc.
As for short z2 workouts, they absolutely do benefit! The term ‘junk miles’ is thrown around a lot but it’s a bit of a myth. There are definitely rides where the stimulus isn’t going to create as many positive adaptions (e.g. 3 hours in zone 1), but all the time you’re riding your bike, good stuff is happening internally.
That’s what I did and why I did it. Without the commute being necessary anymore I can’t justify or motivate the ride time, so prefer sweet spot.
I’ve been doing 45-75 minute Z2 rides all fall - almost every day - 6-7 days per week - 6-7 hours per week average. I was alternating between high Z2 and low Z2 for recovery. A few days of high Z2 in a row and my legs would feel heavy. After that I’d maybe take a rest day or do a low Z2 day for recovery. Occasionally I’d ride outside if it was warmer.
I didn’t make big gains or anything but I don’t seem to have lost any fitness from last year.
A month ago I felt like I had done enough Z2 and started a SS/Threshold progression. It was a really wimpy block that got cut short by family issues but my FTP feels like it popped up 10-15 watts after just 3 weeks.
Haha I am exactly the same. I think it’s the purpose of travelling from A to B. When I was in the office, I’d ride 0700-0900 then 1730-1930. Can’t imagine doing that whilst WFH