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Location: Saratoga calif.
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Bikes: Miyata 610(66cm), GT Vantara Hybrid (64cm), Nishiki International (64cm), Peugeot rat rod (62 cm), Trek 800 Burning Man helicopter bike, Bob Jackson frame (to be restored?) plus a never ending stream of neglected waifs from the Bike exchange.
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friction shifters
In case some of the replies to your question seem confusing , let me try to explain things more simply.
Bikes come in all different types.
In the old days there were only single speed bikes. Then about 100 years ago someone invented an internal geared hub for the rear wheel that had 3 speed gearing. Sort of like an automotive transmission. Sometime later an external set of gears or cogs was placed on the rear wheel hub and a gizmo called a derailleur was used to push the chain between the different cogs . for many years the derailleur was moved by a wire connected to a lever on the frame of the bike. In order for the spring loaded derailleur to stay where the lever pushed it the lever had friction built in to it so it would only move when pushed or pulled. This kept the chain from moving off the selected cog until the rider moved the lever.
As more and more gears were added at the rear it became more difficult to know just what gear you were in. Then someone came up with the idea of putting the equivalent of notches on the lever so it would only move enough between notches to move from one cog to the next. That in essence is what indexing is.
For many years the gearing was 5 or 6 cogs in the rear and 2 Chainrings (the front gears) in front.
With only 2 chainrings it wasn't really necessary to use indexing . Changing the front gears was an on/ off , high / low choice and the lever was either all one way or all the other way.
As even more cogs were added at back and then 3 chainrings in front, indexing became more important and was eventually considered standard equipment on both ends.
With 3 chainrings it is still easy to use friction shifting and many bikes still use it. As was explained above, it is often desirable to move the front derailleur slightly to keep the chain from rubbing against it.
Friction shifting, even at the rear, still has much to recommend it. It is simpler, does not go out of adjustment, and you can theoretically shift from any gear to any other without going through all the gears in between one by on like with indexed shifting.