trans cooler and thermal bypass

[MONSTERMATT]

i installed the supercooler by tru cool , and it came with a thermal bypass, it is gettin to be winter here on the east coast and i was curious to know if it is imperative that i install this thermal by pass in the line? im not convinced i need it, so i would like to know the pros and cons of installing it, since installing the trans cooler i have run at 150 degrees in the 90 deg heat this summer on extended trips, now in the cold weather it barely creeps to 100 degrees , just tryin to see waht could go wrong if i didnt install the bypass