I have kept pushing my card limits higher and higher over the years for 2 simple reasons:
1) For everybody, it is a form of emergency "savings" that can be used if shit hits the fan for some reason. Not too different than the "springy" debt of a HELOC that MMM recommends (that I also use). Obviously it is a horrible interest rate, but as a last ditch effort type thing, it is nice to know it there in an absolute emergency.
2) For me specifically, I travel for work a fair amount and it is not uncommon to be floating $4,000 to $7,000 of airfare/hotels/meals/etc. while I wait for reimbursements to come in so I can pay it off. It is reassuring to know I never have to think about my credit limit if I have to randomly put $2,000 on the card for something out of the blue. I know there is plenty of credit still. When I was doing some remodeling, I made an $11,000 purchase which would not have been possible with a low credit limit. Sure I could have spread it over a few other cards, but why deal with that hassle when the credit card companies have no qualms about giving me a higher limit?
I believe I have $28,000 total in credit between 3 cards, with the highest being $17,500. I have both randomly had my credit limit increased, and I have also specifically requested to have it increased at different times. Any temporary ding to the credit score was really nothing I was concerned about, and quite frankly isn't anything most Mustachians should worry about....