Its a term I have seen over and over again with little explanation. If I
understand it correctly this is a measurement of tolerance for accurate
collmination... is that right?

I came across a table that shows the relationship between aperture, f ratio
and the resulting diffraction limited field diameter. Expert:

8" f4 ~100 arcsecs
8" f6 ~250 arcsecs

In looking at the full chart it appears that the longer focal length the
larger the diffraction limited field of view - really quite dramatic when
comparing an 8'' f4 to say an f8 - a factor of near 4 times.

Some questions....

So? What exactly is the difference any way? Sure an f4 is harder to
collimate but beyond that does this really change the performance of a scope
once it is done well?

How can I translate this into something that means something to me...
What is an Arcsecond and where exactly is it measured? Take for example a
8'' f4 Newt - does this mean my collmination of the light path from the
primary to the secondary needs to be within a 100 arcseconds of where it is
supposed to be? And how does that translate to something I can relate to?

Any input would be appreciated thanks?