I've taken more cold showers this year than ever before. Stop. That's not why.
I found that cold showers are invigorating for a number of reasons. After my workout warm down, I immediately take a cold shower to really cool down. Then it's straight into the sauna to heat back up and stretch. After that, back to the cold shower then into the hot steam room for more stretching and relaxing. For me, this produces an extra adrenaline boost and reduces soreness the next day.
Additionally, I've found that cold showers are an effective mind reset when I get caught in an episode of "stinking thinking". Just try and stay camped out inside your head when cold water hits it.
Today I read that the FDA thinks cold showers can fight the common cold. That's interesting.