This is not really a bidding theory post, it's more of a practical thing.
In my regular partnerships I play very complex systems. But I also play with lots of different people from the club, and then we play simple versions of Acol. Now, I'm not a big fan of Acol, but if it's just for the odd evening I don't really feel I miss anything from my more complex systems ... except for one thing.
Traditional Acol has no bid which shows a forcing raise of a suit opening. If partner opens a major and you have a game-forcing hand with 4-card support, you are supposed to start by bidding a new suit, and then support partner at game level on the next round (a "delayed game raise"). With a very strong hand you might have to start with a jump-shift. (These days splinters have become very popular - widely understood even at the club - but they don't help you when you don't have shortage.)
The problem is that this just doesn't seem to work. Either you or your partner has to guess whether to go past game, and my experience is that it is very difficult to guess well. In order to have a sensible auction, you really need to tell partner that you have a game-force with support before you reach game level. So, you need a forcing raise.
For me this really became very evident in the last few weeks. I saw six hands suitable for a forcing major-suit raise - three in a beginners' class, two in the club duplicate and one in a league match. Of these, there were two missed small slams, one grand played in game, one poor slam going off and one hand played at the five-level with three losers. Only one time was the hand bid to the right contract. But in each case where it went wrong you couldn't say anyone had made an obvious mistake. And in each case the hand would have been trivial to bid with a forcing raise (apart perhaps from the grand slam, which might only reach six).
So it's clear to me now: if you have a new partnership - even for just one evening, and no matter who your partner is - you have to agree a forcing raise. Forget about defences to 1NT or other such trivial matters. You can do without those. You can't do without a forcing raise.
This applies even to beginners. Generally you would like to teach a beginner basic natural methods, leaving any unusual conventions to people who have reached a more advanced level. But for raises it's totally the opposite way round. A beginner is hopelessly lost without a bid which shows this hand, whereas it takes expert judgement to play delayed game raises. This is a rare example of how adding a convention actually makes the game much easier to play. Club players are often criticised for using Blackwood too early in the auction; but in many cases this is because they have no reasonable alternative. If they haven't been taught a forcing raise, what else would you expect?
The good news is that the EBU's teaching methods now appear to be recommending 3NT over a major-suit opening as a "pudding raise" (showing a raise to game without a shortage to splinter in). But this hasn't yet permeated through to the ordinary bridge player in the way that splinters have. A pudding raise is excellent for beginners or for a one-off partnership, though it doesn't solve all problems and so a lower forcing raise would be preferable (but requires more complicated responses). When I played with David H at Cambridge we thought we couldn't afford to give up our natural inviatational 2NT response (I might have a different opinion now!) and so we used 3C as a raise instead. We started winning IMPs every time it came up. I've never seen a convention which made such an immediate improvement to a system as this one did.
This was all assuming a major-suit opening. And indeed it is more important to have an artificial raise for the majors than for the minors. But this is only because of frequency: with, say, 4-4 in a major and a minor, if partner opens the major you need to raise immediately, whereas if he opens the minor it's more normal to bid the major-suit first. Thus a minor-suit raise is only really needed when we have a single-suited hand - but when this does come up it is no less important than it was for the majors. In a simple system I might like to use a jump in the other minor as a game-forcing raise. Admittedly, when it comes to the minors, if you're playing in a one-off partnership you might just hope it doesn't come up. That wouldn't work for the majors though.
I've heard some traditionalists say that you can get by without an artificial raise. Perhaps you can, just about, get by. But as I said, it takes expert judgement to play delayed game raises with any sort of effectiveness. And if you then go and look at the systems the experts are actually playing ... they are unanimous that an artificial raise is a good idea.
So my conclusion is not so much that it's nice to play a forcing raise - because I'm sure you knew that already - but that if you have a beginner who is learning Acol, or a new partner who plays old-fashioned methods, this is one thing you really must add to their system.