What about outriggers?

We are about to purchase a 28 foot boat that will be used primarily for
fishing in the waters off North Carolina. We are unsure about outriggers and
whether they would be worthwhile for us. I know they are used when trolling
for billfish. Are they used for other species too - tuna, mackeral? And am I
right in thinking they serve no other purpose than to let you get more lines
in the water?

Thanks!

--
Peter Aitken