What a resistance band is good for
A resistance band weighs nothing, costs little and fits in a bag. Tension climbs as the band stretches, so the hardest point is the end of the movement — the squeeze at the top of a row, the lockout of a press — which is exactly where free weights get easy.
It is poor at heavy lower-body work and hard to measure: a band gives you no number to beat. Track reps and the tension you started from instead.