Time to put on my serious face. Look, time traveling is knowingly manipulating the game's clock to occur effects that are unnatural to the programmer's desires. I don't suppose "cheating" is the correct term. But...the thing is as long as it's not hindering my gameplay or anyone else's then there's little to know harm in it.
However, time traveling does saturate the online market for things such as the auction house. It hinders action by those who are trying to sell items to other players. Let me explain.
If you time travel constantly, get an exorbitant amount of bells this way (because you can obviously make more money by time traveling than playing the game normally) you can get things that may take some a long time to get. Like a majora's mask from nook's or all the mario series. A player who doesn't time travel may get those things and want to sell them for bells to pay off a mortgage, but so many others got them due to time traveling (and hacking, but that's a different story) and sell them cheaper or give them away for free.
Don't get me wrong, charity's always nice, but it could potentially take away from someone else's fun. But all this being said, i have time travelled before, i time travelled tons in the first Animal Crossing. And trust me the game lasts a lot longer and is way more rewarding without it. Cheating or not, you're cheating yourself the joy of going to Christmas on Animal Crossing the same day you do in real life. Or you see snow fall the same day it is in real life.
But hey, it's your life, live it whatever way you want.
EDIT: Guys guys, the reason the clock is in the game is NOT, i repeat, it is NOT for time traveling it is so you can correct the time of your game, in case you entered in the wrong time, you have moved, or daylight's savings time. I just moved to California from Indiana, and that was a Three hour time changed, if there was no time change clock i wouldn't have been able to change it back.