Always lots of discussion on these boards about the difficulty of finding flat patterns to practice on, and the bad habits people pick up on THS. 

Based on a lot of years experience, I think it is very possible to gain a lot from practicing on house shots.  The thing bowlers need to remember is that the biggest problem for them on tournament patterns is the lack of consistent swing area compared to a THS.  There is nothing that says you have to use the entire lane just because it is there.  Practice adjusting your release and roll pattern so that you can bring your break point in a couple of boards.  Maybe when you do this you even need to tighten your feet up a board or two.  It will seem uncomfortable at first, because swing area is addictive, but with some work you can learn to get comfortable more squared up.  The next biggest thing people need to work on is reducing the axis rotation ( not the rev rate ).  Most pros have done this to a great degree over the past few years, and there is a good lesson their for everyone.

Are these things easy.  No.  If it was easy everyone would do it.  However, it can be done on a house shot if you put the work in.  If you don't want to, nothing wrong with that either.  I much prefer playing short munis in golf with wide fairways and few hazards, because I don't have the time or inclination to work that hard on my golf game, and I like to score.   

what decreasing axis rotation does is make the ball roll more forward downlane. it will cause the ball to have more controlled reaction. instead of going sideways the ball will not have as strong of a change direction. and blend the wet/dry on ths and on sport shots will let you play straighter and tighter angles while blending out the pattern.

The part Bob left out was being able to at least come close to hitting what you are looking at on a consistent basis.  Most bowlers aren't very honest with themselves on how accurate they are or aren't.

I agree that I didn't address repeating shots and accuracy.  However there is a misconception that guys who hook the ball a lot on house shots are all sprayers with not accuracy.  The problem those guys have on tournament patterns is not so much failure to repeat, but rather that very small variations in release or speed get magnified on flatter patterns that are carrying down in one spot and blowing up in the heads at the same time. 

Also one of the biggest misconceptions in bowling is that increased entry angle, achieved as a result of hook is what lowers deflection to increase carry.  What actually lowers deflection is the energy being released by a ball attempting to change direction, even a small change.  For example a ball with 300 rpm and a 20 degree axis rotation will deflect less than a ball with the same rpm and 45 degree axis rotation, even though the latter may achieve a greater entry angle by virtue of having to be projected further right.  The problem with the latter is that more energy is burned off early as the ball makes a bigger change of direction, and slows down more.  That is why we see so many flat 10's as a result of burnout than was the case many years ago when there was so much less friction.

As for using plastic or urethane to practice, that is a very good way to get comfortable with less swing area, but it does not give the best feed back on what kind of release  will allow you to cut down on swing area when you use resin, which is necessary on about 90% of tournament patterns.