Shinkansen seat reservation

How important is it to reserve shinkansen seating in advance?
I saw one of the guide that certain trains has non-reserved seating. How do you find out ahead of time which train has non-reserved seats?

How important is it to reserve shinkansen seating in advance?

It depends on the train and time of travel. A few shinkansen are all-reserved. So, making reservations is essential. Also, during certain busy of the year, trains get very crowded, and a seat reservation can make travel much more comfortable.

I saw one of the guide that certain trains has non-reserved seating. How do you find out ahead of time which train has non-reserved seats?

By reading more about shinkansen and the various lines here:
http://www.japan-guide.com/e/e2018.html
(click on the line names on the map for more details on each line)

If you have a JR pass then reserving tickets does not cost you anything and while not necessary is well worth doing. If you don't have a JR pass then I have never struggled to get on a shinkansen. I have had to stand a couple of times on busy days.

Depends on the train. I have many occasions where my preferred train is full and I have needed to get earlier or later options. Standing is not always an option.

Also depends on how many you have traveling with you and whether you want to sit together. It will be harder to find seats together in the non-reserved cars as the locals are pretty quick to snap up a seat in a separate row.

Non-reserved car numbers are indicated on the right side of the incoming train message boards on the platforms, so you can know ahead of time where to line up.