crystal growth
Once a tiny seed crystal exists, more material can pile onto it the way frost feathers spread out from a single starting point on a cold window. Crystal growth is this steady building-up of an existing solid particle, layer by layer.
Crystal growth is the stage after nucleation in which dissolved ions deposit onto the surfaces of already-formed nuclei, enlarging them into bigger crystals. It competes with nucleation for the same supply of dissolved material in a supersaturated solution.
It matters because crystals that grow large and well-ordered are easy to filter, hold few impurities, and give clean gravimetric results. The analyst tilts the balance toward growth — and away from a fresh burst of nucleation — by keeping supersaturation low and giving the solid time to develop.
Adding the precipitating agent slowly, drop by drop, into a hot, dilute, well-stirred solution favors crystal growth over fresh nucleation and yields coarse, easily handled crystals.
Slow, dilute, hot addition grows large crystals instead of many small ones.
Crystal growth and nucleation are two outcomes of the same supersaturation. Whichever dominates decides the final particle size, so controlling the conditions of addition is really controlling this contest.