In good weather conditions, if an aircraft experiences an emergency on departure, then you can land back at the departure aerodrome. Therefore, before the Commander begins a take-off, the visibility at the departure aerodrome must meet or exceed the required minimum visibility for both take-off and potential landing back at the same aerodrome.

In low visibility conditions, if the visibility is not suitable for landing back at the departure aerodrome, the Commander can still proceed with the take-off provided that a suitable alternate aerodrome is available for landing. In these conditions, this take-off alternate aerodrome must be planned. This ensures that there is always a safe landing option in case of an emergency after take-off.

EASA AIR OPS
AMC3 NCC.OP.110 Aerodrome operating minima – general
TAKE-OFF OPERATIONS

(a) General:

(1) Take-off minima should be expressed as visibility (VIS) or RVR limits, taking into account all relevant factors for each aerodrome planned to be used and aircraft characteristics. Where there is a specific need to see and avoid obstacles on departure and/or for a forced landing, additional conditions, e.g. ceiling, should be specified.
(2) The pilot-in-command should not commence take-off unless the weather conditions at the aerodrome of departure are equal to or better than applicable minima for landing at that aerodrome, unless a weather-permissible take-off alternate aerodrome is available.