Yeah I use it while plugged in. Mostly when I get home after working all day and want to prevent it from running out of power while I use it. I feel like using your phone while it's charging should be considered a fairly normal use case scenario? I mean if that's what's causing my cables to fail early then I would argue that Apple didn't design them durable enough. Speaking of charging, the iPhone 8 is heavily rumored to have fast charging on top of noticeably improved battery life. If that's the case then it may well be enough to save some of that Apple Tax is cable costs.