**Core Concept**
Local anesthetic agents like lignocaine (lidocaine) work by blocking sodium channels in nerve fibers, preventing the initiation and transmission of nerve impulses. However, their efficacy and duration can be enhanced by various additives, including vasoconstrictors and adrenergic agonists like adrenaline (epinephrine).

**Why the Correct Answer is Right**
The addition of adrenaline to lignocaine for local anesthetic injection has several advantages. Adrenaline causes vasoconstriction, which reduces blood flow to the area, thereby slowing the absorption of lignocaine and prolonging its duration of action. This also helps to reduce the systemic toxicity of lignocaine, as less of the drug is absorbed into the bloodstream. Furthermore, adrenaline's vasoconstrictive effects can help to minimize bleeding at the injection site.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a recognized advantage of adding adrenaline to lignocaine.
**Option B:** While adrenaline does have a role in increasing the duration of local anesthesia, this is not its primary advantage when combined with lignocaine.
**Option C:** This option is incorrect as adrenaline does not have a significant effect on the potency of lignocaine.

**Clinical Pearl / High-Yield Fact**
When combining adrenaline with lignocaine, it's essential to be aware of the increased risk of cardiac arrhythmias due to the sympathomimetic effects of adrenaline. This can be mitigated by using a lower dose of adrenaline or by carefully monitoring the patient's cardiovascular status.

**Correct Answer: C. Decreased systemic toxicity**