I used to press that button literally every day and after updating my Opera, i had a little shock for a while.
I always close tabs and need to reopen from last closeds literally every day. I have more than 150+ tabs because of my job currently, still I accidentally discovered "Search in Tabs" feature using shortcut (probably was Shift+Tab but it seems removed) but never used.
That button was one of best features of Opera when I start using it in 2009 and I still love it.
I hope developers find another way to implement new features without making old boys sad.