I think the dangers out there that would cause people to seriously consider taking a 'multi' might include...
* working long hours
* stress at work
* stress at home
* foods consumed that are denatured (rather than boosted) by GM
* junk food offsetting good food
* processing with chemicals that just shouldn't be there
* strenuous training
* insomnia
* too much alcohol
* using recreational drugs
* too much simple sugars/carbs
* compromised immune system
* rehab after an illness
However the dangers out there that might cause a person to consider a 'mega' would include...
* genetic factors > clinical major depression, ODD, OCD, ADD, ADHD, bipolar II, certain forms of anxiety eg. phobic anxiety, anger/rage/revenge, rheumatoid arthritis, etc.
* excessive use of alcohol
* taking and abusing certain recreational drugs
...remembering that even the rationale behind using a 'mega' is still, to augment what the body isn't quite producing or consuming.