Since I play the piano, I use it as an assistant, but then it'll be wise to actually understand all the instruments you use in your composition so your composition won't become something impossible to play.
Also you should try to listen to different sounds the instruments make.
I'm composing a string trio at the moment and obviously composing on a piano wasn't that helpful, it'll only be a guide but I have understand how the string instruments work and what they sound like to actually make it like a string piece.