> Having some kind of centralized travel booking service that "took care of everything" would likely have caused me to find another job
Having worked at both kinds of companies, I vastly preferred having a travel agent that took care of everything.
For example: one time I had a later flight with a layover. The initial flight was delayed on the tarmac before takeoff, and immediately upon landing, a person called me telling me there were no more flights that evening to my final destination, but they'd already booked me a hotel near the airport and the first flight out in the morning to my final destination, and asked me if I'd like any modifications. Perhaps someone else who wants more control would like to handle that stuff themselves, but for me, it was a massive luxury to have an experienced professional automatically smooth over any problem I encountered during my travel. I certainly didn't miss keeping all my crumpled receipts and submitting expense reports either.