It’s only more utility, if those characters need to train for a long time.
If you just want to create a focused alt (eg. PI, trade, research alt, etc.), then you only need to train the character for a short period of time, so MCT makes sense.
But, if you want to train several characters up over a long time, separating them on different accounts is cheaper.
MCT is cheaper long term if you only need some focused alts, because the whole account is Omega and all 3 characters can use all of their skills, even long after you stop training the alts.
If those characters are on separate accounts, you need to maintain separate subscriptions to keep using all of their skills (and skills not accessible to alphas).