For the old, deprecated standard shader, that was true; you needed to make the weights more or less add up to 1.0 yourself. However, for the new standard surface, standard hair, etc shaders they are always energy-conserving and so you don't need to worry about the weights adding up to 1.0. They use a layered approach, where each layer will modulate the one beneath it, not allowing energy to exceed 100% at any point. You can set those weights to anything you like in the range of 0.0 to 1.0 for each layer.
When linking a texture to the base color, if you set the base weight to less than 1.0 you will darken your textured base color a bit. There's nothing wrong with that, unless you didn't expect any darkening of course (and in that case, set it to 1.0). The default base weight is less than 1.0 because in the real world there are not matte/diffuse surfaces that reflect 100% of the light that lands on them; there is always some energy loss. If you've baked that slight energy loss into your texture, then you'll want to set the base weight to 1.0. If you haven't, and you have some pure white areas of your base color texture, then bumping down the base weight a bit to 0.9 or 0.8 is recommended just for realism's sake.
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