I've never used alternate tunings on my guitars but I'm in the throes of learning new material and one of the tunes calls for Open D tuning.

One ... What is the reason for this type of tuning?

Two ... How is it accomplished?

Three ... Can any tune be adapted to this type of tuning?

Four ... If a musician is using alternate tuning, is it best to take two guitars to a gig, one in normal tune and one in alternate tune?

Five ... Can one still use a capo in alternate tunings?

Six ... What are, if any, the pitfalls of using alternate tunings?

Seven ... Any other information, with which you would like to part.

Thank you.