Some people never block. Some people always block.
It really depends on the project and the yarn used.
Ex. Acrylic and durable cotton yarns don't need to be "blocked". Just wash/dry it and it's "blocked"
Wool blocks well and needs to be blocked as washing/drying will ruin/felt it.
Delicate fabrics (cashmere, alpaca, mohair) must be hand-washed and blocked as washing/drying will ruin it.
True lace MUST be blocked, regardless of yarn type, or the pattern will never show/shine through.