Explosion is a useful wallbreaker or revenge killer in competitive matchups, but not really that useful for a casual playthrough since the story battles just aren't challenging enough to necessitate it. If you want to skip Explosion, you could use the extra slot for something like Rest, giving Exeggutor some potentially useful recovery. Also, I don't think Exeggutor has good utility with Sleep Powder/Stun Spore given its low speed, so I probably wouldn't put both of those moves on it at the same time.