Swiss Rail Pass/are reservations necessary?

No, not at all. Trains run frequently and one benefit of the pass is that you can just hop on without additional planning or purchases.

You do not need to, and in 99% of the time cannot, book seats on trains in Switzerland. It is a "turn up and go" service.
The only ones you book on are a few tourist routes, that I could literally count on the fingers of one hand: Glacier Express, Golden Pass, Bernina Express, er, that's about it. And, even on those trains you only need to book if you want the special panoramic coaches or have a meal. The normal coaches do not need booking.

Zürich to Luzern (local spellings) is 2 trains per hour. Lausanne to Basel is one per hour. So just turn up at the station and get on the next train going in the correct direction.

Chris: From the official Glacier Express website:

Seat reservation Glacier Express
Independent Travellers
The seat reservation is obligatory and may be made, at the earliest, 90 days before the proposed date at all Swiss railway stations, at the most major railway stations abroad, at all travel agents selling rail tickets or directly online on this page.

If I recall correctly, the Glacier Express is all panoramic cars. That is not true of the Bernina Express.

as Chris says, you show up find the track and go. You can get little pocket schedules once you're at a station so you don't have to sit around and wait.

Excellent! Thank you all for the advice.
Sue

99% of the time cannot, book seats on trains in Switzerland.

One most always can find an empty seat, but it is possible to reserve a seat on most domestic trains in Switzerland. Details here:

http://tinyurl.com/qhyqc9m