So - if you are using a mixer that only has RCA Phono outs (and even some respected pro mixers like the Vestax PMC-05 only have Phono outs) and you turn up to a gig where the sound system only has XLR inputs then - no problem. Just hook up the outputs of your mixer to the DTI and then hook up a pair of XLR cables between the DTI and the Amp.
Same goes for 1/4" Jack and XLR ins and outs- it will let you connect 95% of mixers to 95% of sound systems. It has the added benefit of being an isolating DI box - coverting an unbalanced signal to a balanced one - allowing for longer cable runs and so forth but it's worth the money just for being able to convert from Phono to XLR in my book.
It is a Stereo box so it can take both the Left and Right signal from your mixer and it's made from sturdy metal so it'll take a good bashing- it's worth pointing out that this is a totally passive device that doesn't need any power and it wont have any effect whatsoever on your audio quality. Like I said - it's the most usefull box in the world- ever!