you don't say what you consider a long time - minutes/hours/days(
) The only problem with extended isolation is that the sub will need to pee at some stage and this really destroys the scene - unless of course you are into diaper-play in which case it just adds to the suffering.
as someone who rather likes this form of play, I like periods of complete isolation with occasional "surprises".
If the isolation is good enough, particularly hearing and sight, then you can creep up on your sub and do evil things without warning, such as apply clover clamps to anywhere sensitive, run a pinwheel over the body (I had this done across my balls,whilst they were tightly tied, and with a Magic Wand applied to the penis tip - mind-blowing !), ice/hot spoon, impact play using mini-floggers, kebab skewer points dragged across the skin.
I find time perception alters when in isolation bondage, so you can do things like tell the sub they must put up with something painful for a certain time - they will have no real idea how long it will last.
I mentioned hearing isolation - ear plugs and hoods aren't totally isolating, so generate a noise in earphones to mask local sound - I use an FM radio tuned "off-station" but you can get white noise recordings for MP3 players as well. Or you can be really cruel and play some music the sub hates, on a repeating loop.