Well, in person has the availability of trying things on. Since even with taking good measurements, not every company uses sizes accurately (for example, you have a 20 inch neck, and shirts might say they're 20, but be up to an inch either direction, or you only have general sizes (sm, med, lg, etc) and not every company treats those exactly the same as all the others. Then you run into online shopping including things from overseas where the standards are completely different.

As an example, my thick-ass neck comes with a thick-ass chest, and in us sizes, I tend to prefer a 3x. A 3x from china or Thailand may be more of a single x, or xxl at best.

So, in person shopping is going to end up with less hassle overall, no matter how well you measure yourself.

I hate in person shopping though. Despise it with a passion, and always have. Giant fucking head, giant feet, giant hands, and until I stopped lifting nothing was ever cut right for my body. Even after I switched away from lifting big, it still isn't exactly a fun process finding things that fit every part of my body right.

If I shop online, I buy bigger than I need usually, because that's just my reality. If I don't, something is going to chafe.

If I shop in store, I at least can find things that fit me better. But the only thing I've ever owned that fit me perfectly is my suit. I sprang for it to be tailored, and made sure it was going to last, with room for alterations as my body changes over time.

But, damn. It's an uncomfortable experience. Doubly so in winter and summer, where either heating in stores gets me sweaty, or the heat from outside has me sweating before I go in, so I have to fuck around until I cool off.