You could easily name tab groups, and view previews of tabs within a group on one screen. It was also fairly trivial to move tabs between groups, when compared to the "joys" of dragging tabs between windows.

Anything to do with browsers could be boiled down to "replaced by using windows" - but there are some definite benefits to sticking within one window.

The tabs don't load into memory unless you switch to that tab group. Also it's much easier to work with one window. You know how before tabs were invented, you had to open each website in a new window. It was a pain in the ass. Tab groups is just the next step. They are like meta-tabs.

II have a tab group for each topic/task I'm working on. I have about 10 groups/80 tabs total, so if I open them all at once it takes a while. With tab groups non active tabs are not loaded right away, so when I'm working I e.g. don't need to open all the tabs where I'm planning a vacation open. I used to use lots of different sessions before discovering tab groups, but it was slower and I lost track of sessions often. Tab Group makes life just a bit easier.

I have a difficulty with separate windows: They all look the same. I'd use a tabgroup for the doc (MDN, StackOverflow), another for the website I'm building (2-3 tabs because you enter data in the first page, view it in the second), and another group for live websites (gmail & co). Total a dozen tabs, well organized in hierarchical manner.

Personally I agree, especially with Mac's CMD+` to cycle through them.

But I guess it adds another level for grouping things that are in the same window but slightly different, or maybe some people are just prejudiced against multiple browser windows..

The only thing I can think of that isn't just down to "how you use it" would be grouping tabs in the same cookie session, but not persistent - i.e. an incognito window with a bunch of tabs you want to organise, but share cookies. That being important seems like a stretch though.

Well, on Mac CMD+` doesn't cycle through full screen windows.

I tend to open a lot of tabs, so it was convenient to have an easy way to group them by topic or environment without closing up my windows manager with multiple FF windows.

If you think about it, tabs themselves are just an effort to avoid multiple browser windows.