For those without a knack for it.. sure... it can be cringe.
As a graphics designer of 30 years, and a sign maker for 24 years, I can assure you I've got a well trained eye for positioning, negative space, balance, rule of thirds and all that stuff. I regularly tape up graphics by eye, then measure to see where I'm at... and I'm rarely off by more than 1/8" at full arm span. Many times on the money or only off by 1/16". In any case, the human eye isn't attracted to precision, especially on a vehicle with few/no parallel lines. It's about perception. You can measure the piss out of something for 10 minutes and try to make it to whatever YOUR idea of perfect is based on what... a PVO template you brought into Illustrator? What's your point of reference when a vehicle has a 'learn forward" position, very few, if any parallel trim pieces, etc. The ground? Is that the measurement YOU think is important? Again, perception. IMO, it's far better to step back 20 feet and actually LOOK at your work before you commit to the install. Unless it's a box trailer, F the measuring tape. Precise measurements are not the end all, be all silver bullet. When YOU are impressed by YOUR work.. that's the time to stick it. Make adjustments for what looks good... not just for your professional pride or your clients first impression, but ultimately the ROI the client will get from having an "eye-catching" graphic in a way that suggests artistry and talent were involved, not just "another print shop with a measuring tape".
P.S. I hope you're not one of those folks who includes punctuation when centering a sentence. /smh