"With regard to grammar, I note that my revered father זצ'ל held that its study is included in the מצוה of תלמוד תורה because its knowledge is crucial for reaching correct Halakhic conclusions. He cited a grammatical error which led a well intentioned author to propose building a מקוה in any Jewish home. Ignorance of the gender of the noun אצבע in רמב'ם הלכות ספר תורה פ'ה ה'ט had led that individual to advocate מקוואות in that were undersized and invalid; their use would have resulted in massive איסורי כרת. Knowledge of grammar is thus not פרפראות לחכמה, which the תוספות יו'ט defines as "studies undertaken to enhance knowledge" also not to be denigrated -- but גופי תורה , 'studies that affect Halakha.'"
R' Nathan Kamenetsky, Approbation for Grammar for Gemara, Yitzchak Frank (Jerusalem: The Ariel Institute, 1992)