Esteps and extrusion multiplier are related, but different, solutions to a similar problem. Changing one value by say 10% should be the same as changing the other by 10%.
Esteps is "how far does the extruder motor have to turn to extrude some length of filament". This lets your slicer know how much plastic volume should be extruded per step of your extruder motor
Flow rate is "crap, different filaments expand/contract at different rates and have different physical characteristics like viscosity".
This is why the extrusion multiplier setting is associated to your filament profile in PrusaSlicer and all its derivatives. I use a much lower value for ASA (around 0.88 if going slower and cooler) than PETG (0.95 ish) than PLA (1.0) than TPU (1.15 if memory serves).
I'll also tweak my extrusion multiplier depending on how I'm printing. For example, right now I have an ASA print going. The printer is laying down filament at 30 mm^3/s. To do this I'm printing a bit hotter than I normally would with this filament (245 vs 230). I'm also at 0.92 EM vs my usual 0.88.