fresh yeast vs. packaged
Measurements are not the same, fresh yeast has higher moisture and is heavier. IIRC, the conversion is something like 60%, i.e. if a recipe calls for 10 grams of fresh use 6 grams of dry. Also fresh yeast has a shorter shelf life and can be a lot less convenient if you're not baking very frequently. Fresh can get moldy and start to die off, and cannot be stored in the freezer (it will turn to goo upon thawing).