Plants can be so crowded that no single individual produces normal growth, causing etiolation and chlorosis.
From the en.wikipedia.org
The physiological relevance of the process is shown by sp1 plants being unable to undergo normal de-etiolation, which is a crucial process during seed germination.
From the nature.com
Understanding the function of these receptors has helped plant biologists understand the signalling cascades that regulate photoperiodism, germination, de-etiolation and shade avoidance in plants.