In:

 Clear[unitize, pick, n, data]
 RandomSeed[1];
 n = -1;
 data = RandomChoice[Range[0, 10], {10^7, 3}];
 
 AbsoluteTiming[Pick[data, Unitize@data[[All, n]], 1] // Length]
 
 unitize[x_] := unitize[x] = Unitize[x]
 pick[xs_, sel_, patt_] := pick[xs] = Pick[xs, sel, patt]
 AbsoluteTiming[pick[data, unitize@data[[All, n]], 1] // Length]

Out:

 {0.521171, 9090641}
 {0.458028, 9090641}