Mixing in key should be a fundamental aspect of any music style, if you want your punters to go home with a headache and ringing ears or for your baselines to crash and clash then don't mix in key. Key progression is important to either drop your floor, bar, venue vibe down a few notches in order to change the mood. Similarly you can give the dance floor, bar, venue a lift in energy without changing the tempo. Key changes are at the core of what makes a good EDM track a great 'banger' and it is also at the core of the greatest DJs sets. Don't be fooled either that the camelot system http://www.harmonic-mixing.com/HowTo.aspx is always going to work either. Use mixedinkey to process your collection, organise your music by genre > key folder's (1A - 12B), drop your tracks into their respective folders by dominate key and you will have a large collection of music to select from. Then always listen in your 'cans' if the two tracks sound great in the headphones then they will sound great on the big system.
