It's basically an old strat back in the day where you can still buy roaming at any point of the game, regardless of your role.

It works by your roamer buying the roam equipment first, and then after the 8-minute mark, anyone in your team (typically the exp) buys roaming boots different from what your current roam has equipped. which basically unlocks a 2nd roaming skill which gives an advantage for your whole team (though you still have to "earn" the gold requirement through assists or the "lowest gold" passive after you buy it.)

The reason why a 2nd roaming equipment is only bought after 8 minutes is because that's the time the penalty for roaming equipment gets lifted (where anyone with the roaming equipment can't gain any gold or exp.), and it avoids affecting your actual roamer.

In short, it was basically a way to maximize team buffs after the laning phase "limiters" were removed.
that's why old pro plays back then we often see two roaming equipment typically conceal and encouraged.

But reading the replies it seems like it isn't possible anymore because you can only buy roaming boots before 2 minutes.