Every stitch takes machine time, so stitch count tells a shop how long each piece will run. Size, fill coverage and density drive it most. A small outlined logo might need a few thousand stitches, while a large, fully filled back design can need many times that. Embroidery quotes are often built per thousand stitches, then adjusted for locations and quantity.
Stitch count also changes the garment. Dense, heavy designs are stiffer, can pucker light fabrics and add weight. Shrinking the design, swapping solid fills for outlines or open patterns, and letting the garment color stand in for a background color all lower the count without losing the idea.
Ask for the count once the design is digitized, and compare quotes on the same count and size. Thread color count usually matters less than stitches, up to the number of needles on the machine. More in the stitch count guide.