However, it is a bad habit that can come back to bite you, so in this era of 160 Gb hard drives and 1 Gig Memory, make a habit of sticking to lossless formats for production.
On the other hand - I have tried very very hard to tell the difference between CD and MP3 @ anything over 190 bps, it's ridiculously hard. And if that bandwidth is devoted to encoding some single sounds ... or a vocal even, it's even harder...then plop that vocal in a mix…*they* just aren't going to know you did it.
BUT DON'T!!!
Unless you have no other choice
To keep this FL Studio related - it as others have pointed out uses the Lame codec, this is the best available bar none!
