If I wore a suit, I would never kneel down much less lay down on the floor to inspect something or observe something that one of the guys is asking me about,, which I feel totally free to do the way I'm normally dressed. I'd be worried about getting pipe thread sealant (aka "bird sh*t") or antisieze grease on my clothes just by getting up against something. And a suit with a hard hat and steel toed boots seriously isn't a great look anyway- who're you kidding?!
The reality is, if you dress well, you're not going to spend as much time in the shop- and in my business, that actually makes you less competent and WAY less useful to the company.
As to why I don't dress up for meetings with clients, if they're coming here they need to see that even the senior people aren't afraid to get their hands dirty, and that our engineers aren't just CAD station jockeys or pencil-pushers- we're selling finished units, not paper drawings and specs. When I visit clients, they see me the same way they'd see me if they came to visit, although perhaps without quite so much dirt on the knees. Our work day here can't be compartmentalized into "office days" and "shop days"- I'm in the shop every day, whether clients are here or not.
My clients aren't in suits either- they almost never are. If they were, I'd probably have to dress better and put on a boiler suit every time I went into the shop, which would suck in the summer. One of my clients has hundreds of millions in personal wealth and I've never seen him in a tie much less a suit on the job.