How important they are depends on your perspective. After getting gas with water in it, or gas getting water in it somehow while in my boat, I had a fishing trip basically ruined by a poorly running boat. No way I'd go without one now.
This is a link to the exact one that I installed on my boat. I have it under the back deck, obviously between the tank and the motor. If I had a video of what I poured out of the filter when I changed it late spring this past year, you'd all buy one. LOL
https://www.amazon.com/Moeller-03332...CA2KSS8EVFTCP4