As already mentioned, oil temp climbs much faster than water temp
when the engine is under high load (because the water has a radiator
and thermostat system designed to hold the temp steady).
Downside is that the oil gets thinner as it gets hotter, and it gets hotter
because it is under high loads. At a certain point, the oil can no longer
maintain a film between the bearing surfaces, and overheating, melting,
and/or seizure will occur
Brief excursions into high temp with a good synthetic oil are unlikely
to cause problems. But extended running at high temps (especially with
mineral oils) will increase wear, degrade the oil and lead to premature
engine failure. Serious race cars have engine, trans and diff oil coolers
for good reasons
So yeah, if you have a race car running endurance events, and you
want to protect you investment, an oil temp gauge is a good idea.
Cheers... jondee86