In cellular respiration, a series of molecules forming an electron transport chain alternately accepts and then donates electrons. what is the advantage of such an electron transport chain?

The advantage of an electron transport chain is that a small amount of energy is released with the transfer of an electron between each pair of intermediates.  An electron transport chain (ETC) is a series of compounds that transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation occurring simultaneously) reactions, and couples this electron transfer with the transfer of protons (H+ ions) across a membrane.

An egg, or a sack of flour