If you have a dandelion problem I would recommend you mulch / mow the dead dandelions you pull back into your yard. Dandelions are a dynamic accumulator which means they are very good at pulling up vitamins and minerals from the soil which they incorporate into their roots leaves, etc. This means dandelions will contain those minerals when being mulched and mowed back into your yard. If you are having a dandelion problem it likely mean your yard needs one or more of the minerals that they accumulate. So my mowing it back in you will feed your lawn and reduce their appear in the future