I think they're just improving roster flexibility, with the short rosters these days, you really don't want a pure DH.
Right now, they don't know what they'll have at Lehigh, both the top prospects but also the AAA plus guys, who'd have thought Wilson would come up last year and give them a solid 98 PA with 130 RC+? Can he repeat that as a platoon corner OF this season? You find out in June whether they're ready to come up and fill in for injuries, in April it's a guess.
Miller could start at Reading and tear apart AA or struggle for a couple months, Crawford could struggle with swing adjustments or the light could go on and he forces a promotion, Kemp might be for real and quickly adjust to corner OF to go with 2B and 3B, Abel could fix what's ailing him and push for a BP role, and so on. And a couple veteran "show me" signings might pay off like Hoffman and Ruiz.
But you can't predict which, if any, of these guys will be able to help you in July, so you have to have enough flexibility to take advantage of a hot minor league player - he may not be the direct injury replacement you want, so you may have to shuffle players around.