we put a pit in my FIL's garage. for all the work and hassle it would have been almost as cheap and a whole lot easier and more useful to have just done a lift. which is why I did the lift route in my shop...
cons we ran into:
while digging, it filled with water, had to pump while pouring,
forms are a PITA and bowed out,
you need to pour a bathtub so it doesn't keep getting wet,
dripping water/snow/fluids are a pain to keep out/clean up,
it gets dirty with sand mud debris and dust so sweeping is a pain
it's dark and full of spiders,
you have to make it really long if you use stairs, otherwise a ladder is a PITA
you need steel edges and grates for when not in use,
safety factor of fumes,
running air/power,
pumping out oil from oil changes if you drain it in a drum,
completely useless for brakes/tires/suspension, transmission work,etc.