Can someone explain the benefit of "scaling in" to me?

I've been thinking about trying this Usually when I enter a position I just enter with my full amount (which is usually 1 lot/100 shares) But I've been trying to understand if there's a point to entering with like 50 shares at first and then adding 50 more if the trade goes my way. I've heard people refer to it as "the small profit from your initial entry helps fund the rest of your entry" but I cant seem to wrap my mind around that concept Why do that as opposed to just entering with your full position size to begin with?