If you're making a tart or a tartelette, you're almost certainly going to use
shortcrust pastry. For a dessert, it's very classic (and delicious), but what about for something savory: a
quiche or a
tourte, for example?
In that case, you'd be better off using a much less sweet shortcrust pastry to
line your mold(s).
Less sweet (20 g vs. 110 g for 500 g flour), but still sweet, wouldn't it be worth doing away with sugar altogether?
The small amount of sugar won't affect the taste (so your quiche won't be sweet, phew), but it will affect the coloring of the pastry, bringing about a beautiful browning at the end of cooking. This browning is due to the caramelization of the sugar during cooking, the famous Maillard reaction.
Put another way, if you don't put that little bit of sugar in, your tart/quiche/tart, or rather its pastry, will remain a little whitish, dull, and therefore sadly unappetizing.
This small amount of sugar (5% of the weight of flour), which you can't taste, but which affects the coloring, is found in almost all doughs that you want to be golden-brown:
shortcrust, deep-drawn,
pizza,
nacho, etc., and you shouldn't eliminate it thinking it's useless.
To sum up: you always need a little sugar in a flour-based dough intended for a savoury recipe, for the sake of beautiful colouring when cooked.