If you're talking about those services which promises to multiply your bitcoins, they're mostly scam.
Here is the simplest answer. It is too good to be true. You might want to stay away from it or else you will lose everything you got. Problem is people got tricked too easy.
Yeah provably better to stay away for those scam there is no legit are giving high roi for your investment .
I experience many times outside in this forum when i was newbie.. so dont trust their word they are lier.