Just conjecture never having used the stuff, but I would think a thick emulsion film like Efke 100 would be good for contact prints/alt processes where you need a denser negative. On the obverse, though, a thick emulsion film tends to scatter the light as it penetrates deeper into the emulsion leading to loss of clarity. This, of course, is not good for those who wish to use negatives for enlargement and who are concerned about image resolution. Under-exposing the negative would help the latter, while increased exposure would benefit those doing contact prints.