I sometimes use the sponge also.Most my work is overskims so i do on 2 coats.
Usually if i got a lot of walls on and its running away from me,ill just give it a light rub up with the sponge and trowel it through to get me back in control then trowel as usual.
Sponge is a good tool to have in ur bag,very usefull on big ceilings were sometimes by the time youve gone over with your second coat it all ready drying and more difficult to trowel /flatten , so in this instance i would use the sponge to get it back were i want it then carry on as usual.
Also if theres a bit of a dent/or miss bit just rub in that area and trowel and its gone like magic !!!
I dont use them all the time and often dont use for weeks /months but will come in usefull now the days are getting warmer.