G1 is the most important phase of meiosis or mitosis.It is the phase when the first cell growth happens.If G1 never happens,the cell aren't mature and DNA chromosomes won't be condensed.The next phase,S phase,take the DNA and copies them.If the DNA never got condensed and mature in G1 phase,S phase wouldn't be accurately completed and then this could result in mutations,and etc.
Hope this helps:)