For driving chisels and adjusting planes (although a wooden mallet is sometimes preferred for the latter). As you go deeper into this craft, your hammer collection will inexplicably grow. I’ve lost count of how many I have now. I think I might have become a hammer nerd. You should see the the one I just got! It has a solid copper head! Anyway, I have found a 375g hammer to be my go-to favorite, but for heavier joinery work I like 570g. Shape is optional but I find the longer head shape to have more general usefulness than the barrel shape.