the main problem with inbreeding (this applies to ANY species) is that there is a higher chance of undesirable recessive traits becoming homozygous which then starts a snowballing effect because once homo that trait is guaranteed to be passed down if that animal ever breeds.
When the Bloodred morph was a new thing there was lots of inbreeding to get more bred and to intensify the deep red colouring, but this caused them to develop feeding problems and they were quite notorious for this. Only through outcrossing to bring in fresh lines has this eventually become a thing of the past.