Singing Warm Ups Are Useless?

I've seen similar studies in the past with mixed results on the benefits of warm-ups. As I've progressed I've found myself doing fewer and fewer "warm-ups" and instead saving my voice for the song I'm practicing.

"This study investigated the effect of traditional vocal warm-up versus semi-occluded vocal tract exercises on the acoustic parameters of voice. Vocal warm-up is thought to be a pre-requisite for optimal singing, but studies to determine the effects of vocal warm-up have found little support for vocal warm-up making a significant physiologic change. Semi-occluded vocal tract exercises are common practice in vocal warm-up that have been shown to cause changes in the vocal tract that lead to acoustic change. One such change is the singer’s formant. The singer’s formant may be quantified through the singing power ratio (SPR), which compares the intensity of the upper frequency formants with the intensity of the lower frequency formants of an auditory signal. This study addressed three questions: (1) Does vocal warm-up condition significantly alter the singing power ratio (SPR) of the singing voice? (2) Is SPR dependent upon vowel type? (3) Is effort affected by warm-up condition? 13 male singers were recorded under three different conditions: no warm-up, traditional warm-up, and semi-occluded vocal tract exercise warm-up. Recordings were made of these singers performing the Star Spangled Banner, and SPR was calculated from four vowels /i/, /o/, /ʌ/, and /u/. Singers rated their effort singing the Star Spangled Banner under each warm-up condition. Warm-up condition did not significantly affect SPR. SPR was dependent upon vowel type, with SPR being most significant for /i/ and /e/. Effort was not significantly affected by warm-up condition."

Original study: https://etd.auburn.edu/bitstream/handle/10415/4004/Duke_Final_Thesis_Draft%203_25.pdf?sequence=2&ts=1450641304137

What are your thoughts on warm-ups? Do they help you? Are they a waste of time?