If there is the direction, you should use the pedal. If no, you can use it too but depends on the situation. Difficult to explain it. Normally, the reasons to use the pedal are make the phrase didn't break on the half way, help you to play through certain part easier ( this may due to the notes' distance ), create a hazy atmosphere and so on. The most important is learn from your experience. Play more pieces. You will learn more from them.

About the classical pieces that you mentioned. If you think the phrase being broke, you can use the pedal to join it. You must dare to try out. Don't afraid. First time with the pedal. Second time without the pedal. If you feel using full pedal makes the piece noisy, try to use half pedal. Sometimes, we only change the pedal after a note being played. Not together with the note and not at the second beat too. That means between the two notes. It is used to join the notes. However, we do change the pedal at the second and fourth beat sometimes. Hence, you need to listen carefully whether the piece sounds nicer with pedal or not. From here, you can learn how to play by ear. Not like some pianists who only know how to play a piece according to notes but didn't aware how does his or her playing sound like.

Actually, the concept is same with the usage of rubato. Although the composer didn't indicate it, you can add it. Maybe yours might be different with others. Don't worried. You won't be deducted mark during exam because everyone has its own interpretation. As soon as it is acceptable, nothing is wrong.