I doubt strongly that Darkness is wasted to simply dispel Light with no additional effect.
Sorry to disappoint.
You have to specifically use darkness to dispel or counter a light descriptor spell.
Light spells are not dispelled "automatically" by the radiating darkness created by the normal usage of the darkness spell. This was a major change in 5e, where that is exactly the case. To use darkness to counter or dispel a light spell in 3.5 or Pathfinder, you have to expend the spell casting to only counter or dispel the one light spell you're targeting, just like a targeted use of dispel magic. Unlike dispel magic, no check is required, however; the dispel happens instantly.
If objects with light spells cast on them of lower level are taken into an area of magical darkness, they stop emitting light while in that darkness, but the spell is not dispelled. If the light spell is of equal or higher level, then the darkness is partially illuminated by your light source. This creates a sort of "surrounded by thick fog" effect, where a person carrying a magical torch (say, with 3rd level continual flame cast on it in a fog of 2nd level darkness) would be able to see around them in the torch's radius, but beyond that point is pitch black darkness.
A note about semantics in rulebooks, and inferring "RAW".
This was the specific issue that the OP ended up having, so I will clarify it here in full for others. In the spell description for darkness, in the d20SRD, here's the exact wording:
Darkness counters or dispels any light spell of equal or lower spell level.
Notice how it doesn't say "Darkness can be used to counter or dispel any light spell". Taken completely out of context, the most logical interpretation is that upon casting the spell darkness, countering or dispelling is included with the standard shadowy-illumination effect of darkness for free. That is not the case.
As a counter-example, consider the logical conclusion of this interpretation. It says that darkness "counters or dispels," so that means that when you cast the spell, you can counter someone's light spell for free, or you can have the radiating darkness dispel light magic. Does the first option sound weird? That's because it is; no spell in D&D that I know of allows you to counterspell and generate normal effects simultaneously. If such spells exist, that would be clarified in the description explicitly. That's just how counterspelling fundamentally works. In fact, the rules on counterspelling state that "both spells negate each other with no results," (from the Pathfinder Core rules) so such a spell would require a very clearly denoted mention that the spell's normal effects persist through the counterspelling. Therefore, we can infer that the best interpretation is that counterspelling is a separate usage, and since the statement is written such that counterspelling and dispelling are bound by the exact same rules, dispelling must also be a separate usage.
Rulebooks are often terrible at semantics, and I haven't looked at the original 3.5 rules in ages but if my hunch is correct, the statement was written differently outside of the d20SRD. Look for consistency in the rules and choose what obeys that consistency; don't pick apart an individual statement. This statement is written in the exact same format for every spell with the same effect. For instance, hallow's spell description reads that it "counters but does not dispel unhallow." It's the same formatting. Even if it's not clear, the meaning is consistent, and we know that through usage of very consistant verbage, the same sort of ruling is applied across all spells that contain this sentence.