The saying is that score doesn't matter in practice because you can't practice carry.  I used to stand behind this very firmly.  Kind of changing my tune now.  With the brutal conditions that have been on the PWBA tour this entire season apart from maybe the US Open and one other stop, lots of discussion has been had about, in Rico's words, taking away the pocket.  "True competitors" champion wanting to make something a "shot making contest rather than a carry contest."  Only problem is that with bowling being a game of transition, it really can't be a shot making contest, it's a guessing game, or basically whose educated guess is best.  Darts can be a shot making contest because everything is the same.  Golf can be close to a shot making contest, weather adds a wrinkle, but at least you can feel or see elements in golf.  But have you ever watched two people bowl on a pair of lanes, one scoring well and one not, and can tell it's not due to accuracy but shape going into the pocket?  How many times have you let go of a shot and know it was gonna hit the pocket but were worried about it carrying?  With the absolute garbage house shots we've had at my home center for years now, shape into the pocket is all that matters.  Hitting the pocket is insanely easy, but carrying isn't.  I can destroy the track in a heartbeat practicing or making videos and have a bunch of 9 counts to show for it. 

Cream will always rise to the top, and carry is one thing bowlers will always blame regardless of the difficulty of the shot.  You could create the easiest shot conceivable and you will still have winners and still have losers, and the winners are the people who figured out how to out-carry everyone else.  I believe it's absolutely a top tier skill and something that's hard to teach.  I have one of the top few averages at my home center now and it's not because I am throwing the ball better or am more accurate, it's because I figured out what to use and how to get the ball to shape up right on the backend to get the pins down more often.  In fact, being "effectively wild" can actually help the shot hold up better than being laser accurate can.
 Thoughts? 

Experienced bowlers who understand how to attack different patterns can benefit just as much from practice on a house shot.  The only thing wrong with a house shot is if it is a steady diet for someone developing their game.  Bowlers need to learn a game that works on long patterns, short patterns and hous e shots. 

Here is another way of looking at it, and something I used to do when I had unlimited access to lanes after leagues got done later in the evening. This is back before reactive urethane came around, but it still is valid today.
I would get lined up on whatever was out there until I could throw 3 or 4 in a row then I would start trying different things to see what would happen. I would find a way to make the ball hit weak and leave a 10 pin (or something else) but still keep the pocket. I would try rolling the ball hard into the fronts, chucking it, tipping it, circling it, tilt with forward roll, soft hand with roll, soft hand with tilt.  Anything I could physically do, I would try.
After a while, I learned that something that might roll like crap on one condition or angle would look pretty good on something else. I got an idea of how to recognize  when a condition looks like it may be ready to allow a certain type of release or attack.
This didn't directly mean that I practiced "carry", but in a Thomas Edison type of way, I learned 100 ways that didn't work to go along with a few that did.
For a lower rev guy, this versatility has come in pretty handy on a few occasions. I still do it when I can, but not like I used to. I still learn things when I get to mess around and try to see what different balls do from all over the lane.

You could/can obviously practice carry on the condition you are bowling on. That may or may not translate to carry on other conditions you bowl on.

Practice should be more about honing a technique than carry. However we are human and if we are pounding the pocket and not carrying it is hard to stay with the technique.

I believe you can have the exact same pattern in two different houses and you will need a different entry angle to carry at each house. Whether this is from the topology of the lanes, of gutter depth, type and age of pins, pin deck material, type of synthetics, how lively the kick boards are, how the pinsetter sets racks, etc, etc, etc.

We used to wonder on wooden lanes how long since the last resurface, last coat of finish, last time the lanes were stripped, is there a dead spot on the lane. With synthetics everywhere now these concerns are now pretty much gone.

The way I have been practicing on THS to make it challenging has been to throw my urethane balls.  If you can get decent carry on THS with urethane you can probably get decent carry on most non heavy oil patterns with urethane and plus it helps you get good carry on THS with your reactives.  The urethanes really place a premium on shot making so you can't rely on the adult bumper but when its there with reactives its a nice surprise.  Plus you save wear and tear and oil absorption on your reactives and I just love throwing urethane.  Come league time though with decent oil in the house they stay at home.