Polite disagree on the latter point, as both a reformed bleeder and a LARP veteran; it's not just about how others treat you when bleeding, as bleed can be self-inflicted/inflicted on others ignorantly or even maliciously - bleeding is as much (IMO even moreso) the responsibility of the bleeder as it is the bystanders/other players/etc. As a LARP vet of some ~15 years (WoD/CofD LARPs too, so I've seen/felt some real bleed in my time), I've never once seen a case of bleed that wasn't dangerous to the player and those around them in some capacity, even just socially. It also never went well for the structure of games, constantly causing discomfort and chafing for many involved. To say that it's not dangerous and based on how others treat you is just not true. If someone bleeds uncontrollably, doesn't tell anyone, and then negatively affects the scene/game at large and hurts themselves/others, that cannot be put on the shoulders of the bystanders. Bleed is 100% the responsibility of the player experiencing it, because roleplaying is a choice, so choosing to RP with bleed that could endanger others, whether aware or not, is on the head of the player themselves.
Now, it's very much worth me clarifying, this is with a stricter definition of bleed than the Nordic LARP definition of bleed-in/bleed-out (due to the social-rules-heavy nature of the LARPs I was in). Bleeding, in our stricter terms, is specifically defined as the negative version of what OP is talking about, (the positive would be more like, I guess, 'blood-letting' - an intentional act done in safe and clean environs, etc). The reason the term 'bleeding' is used is because, in most contexts medically, bleeding an uncontrolled and undesirable occurence that should to be rectified, hence why it's both dangerous, and different, from something like method acting, or 'blood-letting'.
We didn't/don't define bleed as 'you feel what your character is feeling', as that's not having your character's feelings bleed over into your feelings, much like how blood flowing through your veins to/from your heart isn't 'bleeding into your heart'. Consciously taking on feelings is acting. It is wholly possible and common (for many people, but not everyone all the time) to do that without negative side-effects, with some practice/training and mindfulness. Bleed we define as the uncontrolled blending of IC feelings with OOC feelings specifically with the reduced/lack of capability to control those feelings, and that distinction is critical. Bleed is when your character-feelings continue and affect you/others negatively after leaving IC.
With acting, you can and should fully have the capability to 'turn it off' when you go OOC/scene ends, even with Method acting (as someone formally trained in actual method acting, not the 'IC-24/7' abusive garbage some hollywood actors use to justify being cunts to real people). You can intentionally feel the difference between the emotions you feel (as your character) towards another character, and the emotions you feel (as the character that is your real self/selves) towards another person(s), and you can willingly separate them and not allow them to affect you negatively. The moment that the former bleeds into the latter, the IC uncontrollably bleeds into the OOC, that's when you've got a Bleed. (Also vice versa for all this, when OOC bleeds into IC and negatively affects a scene/players, that's still bleed too; the distinction in/out is still present, but not as necessary/critical as the difference in positive/negative or controlled/uncontrolled.)
With that definition of bleed, I will reiterate that in 15 years, hundreds of events and thousands of players, I will truly swear to you that I have never seen a case of Bleed that isn't a negative and a risk factor - in part because we use the term to refer to the negative occurences.
On the OTHER hand, being able to (safely) embody your character and feel their feelings, to really get deep Theatre on that shit, then let the curtain fall, go OOC, and be good (even if emotionally distraught) with your fellow players, THAT isn't bleed; that's LIVIN' THE GOOD LIFE, babyyyyyyyyyyyyyyyyyyyyyy.