If you have noticed most of the seats produced in the last 20 years or so have the cover material sewn to the foam or mesh with a serger.

I do have a serger and I do use it often to finish the edges of furniture fabrics - especially those that like to fray. I’ve used it on the wool fabric insets on airplane seats too. Since it prevents fraying, It makes it stronger and is worth the extra effort. I’ll have to dig through all my pics to see if I have one.

Yeah we use on those fabrics that fray ...it's well worth picking one up second hand if you can. It's one of those thing that will sit there for weeks on end but then when you use it you'll be pleased you have one.

The advantage of serger machine is flattens the edge of foamed piece making next sewing procedures easier. I have tought in buying one.
In this video a master trimmer of Leather Seats.com does a demonstration with this machine (minute 13:37)https://www.youtube.com/watch?v=C3tcrZNKRCc

At a old place of work i used to work they bought one, we was doing very high end stuff and a new serger seemed the way to go...but in reality it didn't work out for what we was doing!

the machine would cut out the panel you marked (leather/foam) and whip them together which you would think speeds thing up but in reality it didn't, unless you need the machine to stop fraying in my eyes its not worth it.

It's good to hear from you again.

Is there a difference between a garment Seger and an upholstery one?

It looks the same but heavy duty for heavy fabrics such as denim, etc.
https://www.pegasus.co.jp/en/machine/detail/series/s103/EXT3216-A04_435K
https://www.youtube.com/watch?v=eaUlzYS1vsk (caterpillart presser foot)
I want to correct my former comment. It is min. 3:37 of the video, sorry.

Interesting to see them gluing leather to headliner foam at Leatherseats.com LOL

Yes, the glue sprayer seems to be soft and not too sticky just to hold the leather piece down and not let wrinkles pop up. I basically do not use this method, I just baste the leather with some points of glue all around the edges leaving it 'loose'.

Well that too but my point was headliner material. We all know what happens to headliner

You are right, it looks like, and we all know how they finish. But perhaps, it is another kind of stronger bonded material.

Unless you're paying 20 plus dollars a yard for sew foam, what you are using for seats is scheduled to rot in the same time frame as headliner foam.