Honestly, it's a waste of time to try and collect every single slug you see. You really only need a few.

IMHO, they're only really useful for speeding up resource extraction from mines. For everything else, it's better to just build more machines than to overclock the existing machines. Better to build two machines, rather than overclock one for double production. So the slugs are only useful for machines that you can't simply build more of, either because there are limited places on the map you can put one (like miners) or because you've painted yourself into a corner with your factory design and don't have room to add more.