One of my other Trumpet Topics pages included a description of the virtues of Long Tones vs. Lip Slurs. Something that I should have also mentioned in that description is that long tones tend to reinforce.
For example, if you are in the process of making an embouchure change, you will probably want to initially lock in on your new embouchure by playing simple exercises consisting primarily of long tones. You will want to establish the new embouchure by playing exercises which you are certain will reinforce that new feeling and not cause you to slip back into your old embouchure, as might be the case with exercises which rapidly move around between high and low registers.
I believe that my Warm-Up is that period which, in addition to stretching -- loosening -- getting the circulation going -- etc., I am really trying to "find my embouchure".
I rarely feel that my first tone of the day is my best. Therefore, why would I want to start off my day by playing exercises such as Long Tones, which would tend to reinforce a less-than-optimum embouchure setting? I believe that it makes much better sense to start off my day with exercises that move around just a bit, allowing me to find that "perfect spot".
If you have been used to starting your day with Long Tones, see how you feel this week starting off with just a few minutes of very simple chord exercises, as in the following example: