When is pump monitoring reasonable?

Monitoring is always reasonable. Pump monitoring is an important factor in the field of system safety, and it is very easy to implement, also as a retrofitting kit.
Because of the reduced risk, this safety device pays off already from the first day of purchase.

Redundantly designed pump stations provide operating safety in case the main pump fails. However, in case of fire or explosion on the pump station, the redundant pump can be damaged directly or indirectly, and redundancy will not be provided anymore. As a direct damage, for instance, a damage of the cabling can be seen, which is often led over the same cable duct together with the main pump.

Finally, in the sense of operating safety, pump monitoring should always be used.