Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said:

But if the imam turns round and sees that the rows are straight and solid (with no gaps), and the people are standing in straight rows, then it seems that he should not tell them to straighten the rows, because that has been done – unless he intends thereby to tell them to keep it like that – because these words have a meaning, they are not just words that are to be said for no purpose.

As’ilat al-baab il-Maftooh, no. 62.