Reserving seats for JR Line within a city?

Hi!

We are spending 8 days in Tokyo & Kyoto; and understanding from previous posts, we should show our itinerary to the staff at JR office at the point of activation so he/she can help reserve everything in advance.

Question is - should we / do we reserve seats for JR trains within Tokyo, or within Osaka? Or just trains from one city to another only?

Thanks in advance!

Actually, you should plan your itinerary in advance with a list of specific trains and times you want to reserve (and some alternative times if the trains are full). At the JRP exchange office the staff will do your current (or next day) reservations, but if busy, will direct you to another ticket office to do reservations for later in your trip (rather than a week's worth of reservations at once).
You can reserve any JR train from any JR ticket office up to a month in advance. Most trains internal to Tokyo or Osaka are non-reserved, and the main reservations you might want are for your long distance travel.

Probably the only case where it could make sense to use reserved seats for intra-city travel (e.g., Narita Express between Tokyo and Shinjuku, or Haruka between Tennoji and Shin-Osaka) is in order to avoid the morning/evening rush. And even then, it's only possible on a small number of routes...