I would consider myself to be extremely passionate, however, I'm very reserved in expressing this passion. It actually makes me feel quite torn at times. Sometimes I desperately want to inspire or encourage others with my passions, but I'm also always keeping in mind that other people may not see things the way I do (actually, they almost never do). Actually a lot of my passions are quite eccentric. So, I usually keep it to myself, wait until an appropriate opportunity arises to get the other person's perspective, understand the context in which they're thinking etc.; If I don't do this first, I might erupt into an emotional mess and lose my focus, or I become very awkward because I don't know what to say, which I desperately try to avoid, and I end up rambling. That's when I would say being passion, in my case, is not all that great. It bugs me sometimes, because this means a lot of the time my passions go unnoticed or unheard, but when someone takes the time to talk to me and dig deep, people are often surprised to find that I'm passionate about a wide range of things.
Some people, in contrast, are actually very good and extremely effective at motivating others with their obvious passion (primalily, I find, types who use Fi as a dominant or secondary function). If they become comfortable socially, they really make an impact just by being themselves. Now, some very passionate people have a tendency to be dominant and overbearing, which can scare people off or make them uncomfortable. That's another case where too much passion probably isn't the best. So, I think that to know what level of passion is appropriate in relationships, it's good to know who you're with and the setting you're in. Within yourself, though, I think passion should be nourished, grown, and supported. It's one of the aspects of life that helps us to grow wiser and make a difference in the world.