This is very true.

The way I figure these things is that I really only want a coin to be up about 6 mm thick if I'm going with a nozzle of 0.4 mm and a general overall width of 35 mm. That way the sides are about 1/5 or so of the width of the coin, and then if I want to do something exciting like patterned cut outs around the edge or some sort of knurling I have enough material to work with but not so much that the whole thing gets complicated and to little detail to actually print.

It's a fairly narrow path to walk.