Breaking the Rules
Breaking musical rules can be great to create musical structures that sound fresh and interesting and basically every rule in music can be broken. The essential part is to be confident and consequent when you break them. For instance if you use a “wrong” chord (for instance combining sus4 and major 3 in one chord) only once, it will sound like an error. However if you repeat it or even make it a prominent feature in your piece it will sound deliberate and become a musical feature of your piece. This will not necessarily make it sound prettier but it will be perceived as desired effect.
Everything that sounds “strange” if it appears only once needs to be repeated in order to make clear that doing that is part of your musical idea. If the breaking of rules actually generates something of listening value however is another discussion.
Of course all that requires you to actually know what rule you are breaking so knowing your fair share of music theory etc. is essential to be able to use a concept that goes beyond that.