being able to loft the front and place it where you want it is a vital skill for technical trail riding. you aren't getting over any decent sized logs, rocks, etc. without being able to do it.
you are also eventually going to bury your front in some mudhole or rut and superman over the bars if you can't do it.
comes in handy on the street once in awhile, too...for getting the front over potholes, etc. (though you can usually just go around them or just ride through them and take the hit instead if you want.)
being able to ride wheelies for long distances is not really useful in and of itself. however, the balance, throttle control, clutch control, rear brake control, etc. involved is very useful for all kinds of riding. so, while i would not say it is a very useful skill in and of itself, it certainly does hone some basics that can save your ass someday.