“Exciting aliases” means capturing detail so fine that it reaches or exceeds what the camera sensor can accurately sample. When that happens, the sensor can produce false patterns or false color instead of the real detail. This is aliasing, and moiré is a common example.

A very sharp lens can make this more likely because it resolves finer detail and sends it to the sensor more cleanly. If that detail is beyond the sensor’s resolution, aliasing artifacts may appear. A softer lens may hide the problem simply by blurring that finest detail.

This is why some cameras use an anti-aliasing (optical low-pass) filter: it slightly blurs very fine detail before it reaches the sensor, reducing moiré and other aliasing artifacts.

So it’s not “good” or “bad” by itself. It’s a side effect of having enough sharpness and subject detail to challenge the sensor. It matters most with repeating fine patterns such as screens, fabrics, fences, and distant grids. In normal shooting, it’s usually only something to watch for in those situations.