Pointless, Unfounded, Careless
な adjective
いいかげん
このサービスはいい加減すぎます。いい加減、改善をするべきですよ。
This service is clunky. It's about time for some improvements.
あんないい加減な人とけっこんして二十年もけっこん生活が続けられるなんて信じられない。
How have you stayed married to such an irresponsible man for twenty years? I can't believe it.
ねえ、お父さん。お母さんさぁ、近所の井戸端会議で仕入れたいい加減な情報に踊らされるの、いい加減に止めるべきだと思わない？
Hey, Dad. Don’t you think it’s time for mom to stop being manipulated by pointless gossip from idly chatting with the neighbors?
You add and you subtract. This brings you back to zero. There was absolutely no point in doing those actions. Completely pointless. In fact, I'd say that was downright irresponsible of you. The extra いい is there to mean "good," as in "good, you've figured out how pointless that was, now stop."
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.