I'm another one who starts early. Not because of the money, but because it's more relaxing to buy little and often. I'm a teacher, and the autumn term is incredibly stressful work wise, so I often start picking bits up in the summer when I have the free time and am not at work.
Certain items I wouldn't buy until nearer the time (main presents, the daddy items (like unicorn stuff), but there are certain generic presents my dc like their stockings such as stationery bits, makeup, smellies etc.. so if I see something I know they'd like, I it it and put it away until Xmas.
The other reason is that I have 3 major birthdays in Nov /Dec (DH and DC) so would find it stressful having to buy all the presents + organise two birthday parties + all the other stuff that comes with Christmas - Christmas play, parties etc etc...
This means that when Nov comes, it's not all a stress organising birthday parties, Christmas etc etc, and I can enjoy it. By and large, most years I finish buying all my presents by end of Nov, so tree can go up first weekend in December, and I can relax and enjoy Christmas.
But then, I'm one of life's planners. Booked my 2018 holiday last year, and am currently planning my 2019 holiday.... but the OP probably wouldn't like this either!