No, really. Do Rae Mi Fa Sol La Ti Do times 200? Boring. Tedious. I could search for other synonyms here but I’m lazy.
The trick is not to play them exactly the same way each session. Who says they have to be played straight, in phrases of four? Change the rhythm (swing? 6/8?). Change the articulation (intercharge staccato and legato). Change the volume. Change the tone quality. If you’re on the piano, play around with the sustain pedal and different patterns you can make. Again just for pianist, play just the melody in one hand with the chords implied in the other. Play the piece backwards. Loop a bar four times, move forward two beats and rinse and repeat. The world is your oyster, and it’s up to the musician to mix and match and make boring-but-necessary exercises fun.
This need not apply just to scales either. Both exercises and pieces can benefit, and you might find you know them far better after screwing around with them than before. Fuzzy statistic: in language, you need to hear a word in 20 different contexts before being unable to forget it. The keyword there is different. Who’s not to say the same doesn’t apply to music? By changing the way you play, you’re reinforcing your knowledge of the music in different contexts. Not that that’s been proven or anything, but at the very least, I feel I’m getting better faster!