Reserved Seat Fee

Hi,

I'm looking at the train schedules on hyperdia.com and note that the fare for some trains include a seat fee. Is it always mandatory to pay this seat fee? Does it mean we will have to take another train which has no seat fee if we do not want to pay the seat fee on the preferred train? Or will all trains come with at least 1 car with unreserved seats where we can try and get a seat on a first-come-first served basis?

For info, I'm considering whether to buy the JR Kansai Wide Pass for my coming trip to Japan and note that the terms state that the Pass does not cover the cost of reserved seats. I was wondering if my travel itinerary would be upset if I choose not to pay for the reserved seats and I end up not being able to travel on my preferred trains. Since I plan to use the Pass to cover some long-distance travel (to Amanohashidate, Kinosakionsen and Tottori), I will have to include the cost of the reserved seats to determine if the Pass is worth-while.

I look forward to your early reply.

Thanks.