To cut corners or slack off — to do less work or make less effort than is required; can also mean to go easy on someone (hold back effort) in competition.
仕事で手を抜くと、あとで大きな問題になります。
If you cut corners at work, it will become a big problem later.
試合で相手が手を抜いているのに気づいた。
I noticed the opponent was going easy on us in the match.
ここで手を抜くと、せっかくの努力が無駄になるよ。
If you slack off here, all your hard work will be wasted.