Typically when people use 3 decks, they only occasionally have all three running at once, or use one for scratching / queuing up the next tune.
I wanted to test out using all 3 properly, so start with 2 tunes playing at once and never have less than 2 tunes playing at any point. Not a great example of my sound, but a fun challenge none the less.
Consider that a typical 70min mix CD might have 12 tracks, with each of the 11 mixes lasting between 30-90 secs, that gives about 10mins total mixing time. This 30 min mix is mixed on 2 decks for the full 30mins, as well as having the 3rd deck playing on top for about another 15mins, giving 45 mins total mixing (or 60 mins, depending on how you do the maths), meaning it has between 4-6 times as much mixing as a normal CD, but done in half the time.
All this fuzzy logic aside it is way more than 12 times harder than normal mixing, and to actually make something listenable is quite a challenge,and I am still not sure I have succeeded.