Unless you're a competitive powerlifter, you don't have to perform your deadlift from the floor. Anyone who states otherwise is an asshole... and probably doesn't train people for a living.

I'll often implement block pulls with people if they have a mobility restriction or are otherwise unable to get into a good position to pull from the floor.

Likewise, block pulls tend to have a better carry over to the deadlift (compared to rack pulls) because you're then able to pull the slack out of the bar. Moreover, depending on where you tend to stall – mid-shin or at lockout – block pulls can be individualized to address that issue.

Related:  The Deadlift's Dirty Secret

Related:  30 Days of Deadlifts