For leisure flights, I book them whenever I decide to go somewhere, especially if paying cash (instead of miles - there's always the Any Seat mileage). Every now and then I might decide to hold off if I have a reasonable confidence a sale is coming along, such as this summer when I decided to fly off for Thanksgiving. LH
wanted $4,000 in C. I thought about using miles but I decided to wait for a "fall sale" (or something) and I was able to book the trip for half the original cost three weeks later.
For work, it entirely depends on the circumstances and what our CTM expects the demand to be on the flights that we want, with the results that a few flights get booked as soon as they're available for booking (if need be, we change the name of the passenger later), a few are booked at the absolute last-minute, but most are booked between a month and a week prior to departure. The main driving factor is when the trip is confirmed, which can be months in advance, or a mere day or two prior.
When I was green, I once entered an itinerary in my calendar complete with times and flight numbers before a trip was confirmed, but that was the routing I wanted. When the trip was confirmed, I totally forgot my calendar entry was only what I wanted, and I didn't request the tickets. I ended up trying to check in for a flight I had never booked to begin with...
Recep Tayyip Erdoğan has no clothes.