Ok, let me give you an actual example of how it works in my case.
I'm on site at, say, a customer based in an out of town business park in Plymouth doing a routine planned software upgrade and expecting to be finished by about 2PM, so I haven't taken any evening meal with me because I'll be home by about 5 or 6 PM (I live in South Wales)
Just as I'm about to walk out the door, the phone rings, another job has come in, our kit at a customer in Bradford is not working and they are screaming blue murder, losing money blah blah blah you know what users are like but they have next day response in their contract so I have to deal with it, I nip back to a desk and book a hotel in Bradford and then just as i'm about to leave the boss at my current location has found a few things that aren't working right after the upgrade, usually these will be things that they were told about in advance with instructions on how to deal with it but I still end up having to show them manually, it's now 3:30 and I'm finally leaving Plymouth.
I have to get to Bradford by 9 if I want to be able to eat at the hotel (on the company hotel card) so I have to get a shift on, can't really afford any stops or detours ideally, but I should just have time to stop at a services and grab a sandwich so I'm not starving for the entire duration of the trip.
Unless you're expecting me to set off on Monday with a weeks worth of packed lunches (and evening meals) in the car and throw out the ones I didn't eat on Friday I'm going to end up having to eat at a services at some point.