It may seem insignificant individually, but 150kgs at todays price of around $1300 tonne is $13*15 = $195 per sector.
Multiply that by, in Ryanair's case alone almost 1000 sectors per day and that's $195 000 per day wasted.
Factor in Easyjet, Baby, BA, Virgin, Jet2 etc and you are looking at hundreds of thousands of $ per day simply discarded.