That would be gut loading. That is, filling them with food that is high in nutrients other fish need but otherwise would have a hard time getting.
Power feeding is dicey, it's a fine line in feeding just enough to match their metabolism and over feeding. A full grown fish has little use for this (I didn't say no use). I usually use it conjunction with a higher temp to increase the fishes metabolism. The only down side (as noted above), is that with higher metabolism and higher feeding (while you may see increased growth) is a higher output of waste (more in=more out).
This is a common trade practice by most trade dealers. Faster growth means higher turnover. More fish go out the door with available tank space thus a higher profit. This should be seen with caution because less than reputable dealers use this practice but not the heightened tank maintenance required, leading to lower quality and not as healthy stock.
