It depends. If you plan on buying the DLC for a game then yes, since you'll have all of it at a discounted price. If you're NOT going to buy any DLC, however, it's a complete waste of money.
Basically. Usually it's all the "big DLC packs" for one lump price, which nets you a "free" DLC pack in there. Like with Borderlands 2, the season pass is $30 for 4 $10 DLC packs when they come out. If you only want one or two, then buying them piecemeal saves you money. If you want three or all four, then buying the season pass is the more economical choice.
You ever meet one of those Don Quixote types and just wonder "What the hell are they thinking?"