Pressing and steaming differentiate great garments from home-made looking ones probably more than anything else. Mismatched plaids and stripes, uneven hem, and wrinkly sleeve caps also say “home made” instead of “tailored”, but not to the same degree, as it takes a bit of scrutiny to see those things. Unpressed seams, however, says “done at home” as much as a bowl haircut on a kid! It only takes the briefest of glance to see the puffy seams, bulging darts, and overly thick collars.
Here is an example, from a “project” page of an on-line fabrics store. I have removed identifying info so as not to shame anybody! I feel this is particularly egregious example of lack of pressing because this jacket could have been so amazing, being made from a “selvedge denim” costing $18 a yard, which is actually more like twice that expensive since it’s only 31″ wide! Pressing and steaming is super easy and very satisfying with denim because it takes a seam so beautifully, being 100% and reasonably loosely woven. Granted, it’ll take a bit of extra work to pound the thicker areas such as where seams intersect, etc. to make the finished seam as thin as possible, but it is always worth it.
Even a jacket that I made from fleece (top pic, above) can be coaxed into having flat and pressed seams by having flat felled seams as well as having interfaced cotton facings.