It's a bad thing because pressure is pressure, rubber expands and (and overtime will swell) under pressure.. it can only expand so much until the least path of resistance is the area where the hose is physically clamped to the cooling system which forces the hose to blow off (even if the hoses are really clamped down, the next path of least resistance is the hose bursting), and from first hand experience at the track it's always the lower hose which is in a pig of a location with GTRs (R32s at least), you're not going to be able to reconnect it with the enginebay still hot, even with it cool it's still a difficult job with everything else in the way. Also because hoses decay from the inside out, outside observations are useless.
The factory OE rad cap is designed around the fact that (1.2bar for turbo apps, alittle under 1bar for N/A apps) this pressure is safe for the hoses to be securely clamped down.