If you understand the relationship between boost and EGT a set of gauges can be a helpful diagnostic tool.
My truck had a cracked intercooler boot and I would not have known it without gauges. The EGT was higher, above what Cummins recommends, and the boost was lower than normal, but it still pulled well.
Without gauges I would have operated the truck under those conditions for who-knows-how-long. The engine probably would have been fine, but 1400 degrees EGT is too high for long-term reliability.
Knowing critical parameters measured against their limits is always beneficial.