Is there any added convenience in using a Swiss travel pass as compared to the half-fare card? Can I, for example, just get on the train and work things out with the conductor and pay with either option, or do I need to book ahead using the app etc? I realize advance reservations are required for scenic or premium routes. Thanks.

The Swiss Travel Pass is your ticket, you just get on the train no further action required. Make sure you have your passport with you, you may be asked for ID, photocopies are not allowed it has to be the original. I would also advise costing all your travel and seeing if the Swiss Rail Pass is the most suitable. If you are intending any mountain trips you will need to buy tickets the Pass is only valid to inhabited places in Switzerland, ie Murren,but not above, likewise Grindelwald but not Grindelwald First and you only get a 25% reduction on the trip to Jungfraujoch from Wengen or Grindelwald.
On the boats it's worth paying the extra for an upgrade to 1st class which is usually less crowded.

With travel passes, you can board and travel. Make sure you are not in first class with a second class pass; you must be sure to carry original forms of ID. Half-fare cards are different, of course, with tickets paid for before boarding.

Thanks to all. Like many, I struggle between Travel Pass and Half Fare Card. I am a horrible analytic. And at my age I value convenience and would like to just get on board whatever vessel/vehicle and pay. Going from Zurich to Montreux, spending six days; Lauterbrunnen for three days; back to Zurich. Eight day travel pass is about $477. I realize there will be additional fees. I suppose even with the Travel Pass you have to spend time on the app making reservations and getting tickets. Too many options!

No need to make reservations apart from the panoramic trains. On most journeys you can't make reservations. Definitely for any mountain trips only reserve for the Jungfraujoch trip from Wengen upwards and do it the night before, if the weather is suitable, certainly no sooner. The trains are so frequent it is just no worth reserving.

It's pretty simple with the Half Fare Card as well...just buy a ticket on the app before boarding. The SBB app is a wonderful thing indeed.