Well, I can have 100s of comps that all adjust to precisely the same value. However, the comps are really there just to estimate the residual for the subject. - Once that is done, putting a dozen or so in the Sales Grid is just to demonstrate how good the model is, that is how low the gross adjustments are, and why the differences in sales prices between the subject and selected comparables.
That is, I use 100+ comparables to create the regression model and score the subject, then select a smaller number for the Sales Grid—for demonstration purposes only.