Hiding gear is naturally more work and expense and makes changes much more difficult than when everything is left out on the floor or an open rack.
On one hand it is probably better to put things away and expose them to less vibration/dust/kids - keeping everything neat and tidy. On the other hand, poor ventilation may shorten equipment life and unless you automate gear and use remote repeaters then you will probably end up leaving the cabinets open during play anyway - which looks uglier than leaving everything on display in the first place.
Does it affect the sound - probably not enough to matter either way unless you are with vinyl or tubes - both tubes and vinyl can pick up acoustic feedback and will benefit from acoustic isolation.
On one hand it is probably better to put things away and expose them to less vibration/dust/kids - keeping everything neat and tidy. On the other hand, poor ventilation may shorten equipment life and unless you automate gear and use remote repeaters then you will probably end up leaving the cabinets open during play anyway - which looks uglier than leaving everything on display in the first place.
Does it affect the sound - probably not enough to matter either way unless you are with vinyl or tubes - both tubes and vinyl can pick up acoustic feedback and will benefit from acoustic isolation.