I noticed this as well. I hope that it's only temporary, as it was one of the few useful tools remaining, but with it actually being disabled rather than just hidden, I fear that it's gone for good.
As for why one would use it, I sometimes like to look and see what other items a new-to-me buyer has made when I get an oddball offer from them on one of my items. Just another way to make a quick character judgment sometimes when the buyer is otherwise unknown to me. For example, if they're giving me down the road for daring to ask $1000 for something, and they offer to "take it off my hands" for $200, but I look at their history and it shows they have never bought anything over $20, it's really hard to take them seriously.
It can also be useful in some cases for investigating unusual and shill bidding, and as Tom said, just seeing what your buddies have bought lately to see if they need an impromptu "congrats!"
Oh, and it's also useful for stalking Tom and making off-Bay offers to anyone he's buying Louisville Colonels stuff from
I say that jokingly, but I understand that scenario has played out many times (even among Net54 members) with competitors stalking each other to interfere with the other's eBay dealings.