From my experiences with HOs ... wait that sounds bad doesn't it. Okay Heroic Opportunities - the categories are: damage (encounter or AE), group beneficial (buff, heal, power), or mob debuff.
There are common, uncommon, and rare combinations (frequency with which you will get them to occur). You are casting spells ANYWAY, so why not do HOs. I've never understood why so few players use or take time to understand this aspect of the game. ;) The only time you may not want to do them is if you are in a situation where you really have to watch AEs (i.e. not cast them) or you have to not do damage. Other than that you really should be letting these fly like crazy.
Scouts are the best class to start Heroic Opportunities and are really the HO Masters - yeah you sexy scouts. When a Scout starts a Heroic Opportunity any other class can trigger the bigger wheel to pop up ... and the only time you will get a chance at one of the uber 4 step HOs is if a Scout starts the chain.
If I'm in a group where the scout clearly hasn't developed a love of HOs, and I'm co-healing with another priest - typically the two of us alternate HOs like crazy fools while casting. One of the really nice Priest Scout combination HOs is a group haste buff....although looking at the EQ2 wiki site some of those are wrong, so guess I'll have to spend some time working on updating that info.
Anyway, some really great things to be had from HOs (free power, free heals, free damage, free debuffs) ... I know it's typically not a MASSIVE amount. But when you consider you are casting spells anyway, why you would choose NOT to use them or understand how to trigger the HO you want to get absolutely escapes me. If nothing else, cast the starter and let whatever happens - happen.
Vallar (90 Mystic)
Guild Leader - Devil's Rejects (Guk Server)
http://gukrejects.guildportal.com