SSO, QLD, DDM vs. SPY, QQQ, DIA

When you have time (no rush) can you explain why you use SSO, QLD, DDM instead of SPY, QQQ, DIA?  I don't have a good understanding of what they do but I have heard that the leveraged ETF's are not meant to be buy and hold positions.  Something about they rebalance and will overtime loss value?
Thanks in advance!