Variation in Training

Hello guys and girls,
I’ll keep the question as short as possible. Both in powerlifting and bodybuilding world there are two competing " philosophies " of training. One says that to get bigger and stronger you have to mix up your exercises as frequently as possible, some athletes ( especially those in bodybuilding ) will go as far as change there workouts for the respective muscle groups every single week.

The other group of athletes say that in order to increase strength and muscle mass you have to stick to certain exercises and try and " master them ", because if otherwise (employing the first method ) your muscles are going here and there and everywhere with no specific emphasis on anything .

Which idea do you ascribe to ? I know everyone is different and what works for one person might not work another, so I’m asking for your " subjective" ( personal ) view. Thanks in advance guys.