If you are flexible about meal times, restaurants and don't mind waiting occasionally, you shouldn't have trouble finding a good place to eat even if you do not make PS ahead of time. There may be times when you will not want to wait for your first choice of restaurant, however.
We've visited several times during the early part of December. I only make advance PS for "must do" places and events, or those that are hard to get (such as CRT, CP dinner Package, etc.). I often stop by the resort's Guest Services Desk first thing in the morning and have always been able to get a PS near the time we want to eat that day in a restaurant of our choice. This has occasionally kept us from a 30 - 45 minute wait (based on what I overhear the CMs tell walk-ups).
FWIW, PT and LTT are among the more popular restaurants. You could end up waiting a long time without a PS or you could notice that walk ups are being seated without much of a wait. You just never know. In early December, it's a good bet that you will not need a PS more often than you will need one. Of course, if you want CRT for breakfast or the Chef's Table at V&A, you better have a PS!
You can always cancel a PS if it doesn't work out for you once you get there. My advice (if you really want LTT or PT) is to go ahead and make a PS. Cancel it if the day/time ends doesn't work.
Enjoy your trip!
Anyway, hope this helps!
