I'm a shade-tree hobby mechanic.  This shirt very nicely supports my hobby, especially when outside on muggy days.

It breathes.  Fit is loose enough to where I'm not constricted, but I don't have shirt pieces dangling over moving machinery.  The fit is enhanced by the material, which wicks sweat off of me as well as helps ventilate.  It's comfortable, even over long work days.  I chose the black color to help with staying cool (literally and figuratively) - the dark color absorbs heat from the body and with the looser fit it all works great.

Another point for the black color - grease doesn't show.  If you care about such things.

Washes easily, very little care required, and just makes this hobby mechanic look like a professional.  I love this shirt.