Playing Acol, you may have a problem as responder with a balanced 10 count, if you are unable to bid a four card suit at the one level, since 1NT shows 6-9 except over 1, and the 2NT rebid shows 11-12. You are also in difficulty with a balanced 3334 hand with 6-7 points if partner opens 1, when a raise in clubs takes you past what may be the best contract of 1NT. This can be true of both minors if you are playing "inverted minor" raises.
All these problems can be solved by making all 1NT responses 6-10 points, (which also means that a 2 level response can show at least 10 points and a good 5 card suit or 11 points with a 4 card suit). With this wider range, if opener wants to make a game try, 2 can be used as a conventional enquiry.
In response, 2NT shows 9-10, a 3 level bid shows 8-9 with a six card suit, and 2 bids 6-8 points, with 2 of major = 3 card support for partner or 2 = 5 cards if partner opened 1, and 2 = none of those). 2 is rarely missed as a natural bid (2 followed by 3 is "I wish I'd never heard of `Wraight'"). The convention often proves useful, both to bid some simple hands which are otherwise surprisingly difficult, but more importantly to be able more frequently to stop in 1NT when this is the right spot.