The biggest reason for not pitching too warm is to prevent off flavors and production of fusel alcohols. If the yeast is pitched at very high temps (>120*F) it can kill the little guys. If pitched warmer, the growth phase will occur too quickly and will produce ester formation and fusels which lead to poor beer outcome.
Beer clarity isn't really impacted by pitching temperature. That is more a result of getting good hot break during the boil, good cold break (by quickly cooling the wort), using fining agents (Whirfloc, irish moss, etc) and cold crashing at the end of fermentation.