Yes, it is much nicer to resign than keeping your opponent waiting the time it takes chess.com to declare the game abandoned.
Some people don't realize this.
Some forget.
Others, don't care.
Others, hope you will leave the game so they can pop back on, make a move and win on time. (Not the way I would want to win.)
If you are losing and don't want to finish your game, don't click the little x in the corner of your tab, click resign!!