As a licensed psychotherapist with a job making 70k a year and only working 5 hours a day 4 days a week. That is... my expert opinion is that Cannabis affects different people in slightly different ways but overall it's a much safer alternative to alcohol and many pharmacuetical interventions... has many medical applications. As far as opening your bronchiols and helping you to breathe your supposed to use a vaporizer so your not inhaling the carcinogens and clogging things up. The cannabinoid receptors are triggered and this shuts down part of your memory system allowing you to remain more present and focused on the task at hand without being overwhelmed by the past or the future as some of the research shows. It also releases a lot of chemcals which are aprt of your emotions system... because it releases a lot of these you feel flat for the next day or two until these natural chemicals are replenished. Like anything else in moderation smoking is a great way to relax and clear the mind. Too much use which leads to anxiety and agitation is because it interferes with sleep and doesn't allow the amygdala and the sleep system to process life events which leads to a lot of junk lying around unprocessed in your brain.
Anyway... smoking weed isn't a bad thing it's a just a chemical that should be understood and enjoyed in moderation.