I mean, how much higher? I'd say this isn't a good practice for BR management (if we're getting as technical as OP is about it) in the long term as variance and just hand strength can crush you short term.
Only a stake or so above what I'm rolled for. It's honestly great for your
bankroll if you know when/where to take these shots and have a solid strategy for playing poker. Of course, I wouldn't suggest for buying in for half your roll at 3 stakes above what you'd normally play just because there is a fish in it. That would be ludicrous. I'm saying that if you see a fish that's playing at a stake or so above what you're rolled for, take what you're willing to lose from your BR to take a shot at stacking this fish for a large percentage of bankroll inceasement. Sure you might be on the negative side of variance and get cooler, but if you're smart about your stake jumping this can be incredibly profitable.
Example of what I mean: I was properly rolled for 5NL at the time, I had about $134 in my account or about 27BI for 5NL. I always have taken an aggressive stance to bankroll management at the lower stakes since I play better than most at those stakes (27BB/100 over about 30k hands over the summer playing a mix of 2NL/5NL). I know that's not a huge sample size, but I was crushing the games and not just because I was running hot.
So, I saw a fish at one of the 10NL tables who I knew was a total spewtard and would call down with third pair and gutshots and stuff like that. He played upwards of 65% VPIP and was a prime candidate to increase my bankroll quickly. I go in with the intention of spending $20 or 2BI at 10NL, and if I went busto with those I'd go back down to 5NL and stay there until I was properly rolled again. I ended up winning in the game for about $30+ dollars over a couple of hours, mostly thanks to the fish. While this won't always be the case, it would be too nitty to pass up on an opportunity like this. Again, you have to be confident in your play and be smart about how you take shots...don't try to make up for losses or anything like that. But taking smart shots even when you're not properly rolled is a skill a lot of players should work on, especially at lower stakes where they will still have a skill edge over the majority of players at one stake higher than they're rolled for.