No, the correlation is irrelevant.

You will get a performance diference between using N to make a string literal NCHAR and not using it so that it is CHAR. If you are comparing with a variable or an indexed column, the performance difference will be so small you won't notice it and probably won't be able to measure it because the number of conversions required is very small; on the other hand, there may be times when the need for conversion makes a big difference, so it's always safest to make sure that your literal is NCHAR if the column you are associating it with is NCHAR or NVARCHAR and not if it isn't, to avoid performance problems.