For the base cabinets, if you run 2x6 blocking flat, ( 5-1/2" side facing the cabinets and center them on the height of the cabinet, you'll have fastening surface for not only the cabinets, but backing in case you need it for backer board or other substrate for the back splashing. Uppers can be 2x4 top and bottom.

Another option if you have 2x6 walls to attach to is to let in,(knotch), a 1x6 for the bases same as blocking and 1x4's top & bottom for the uppers. They would be a band let-in,(knotched) across the stud spaces flush to the outside of the studding. I wouldn't do this on a 2x4 wall as it will weaken the studding.

I've never blocked for cabinets nor have any of the many installers ever suggested or looked for it. I suppose it can't hurt, especially if you get an installer who can't locate the studs.

If you go the let-in route with 1x's, instead of trying to knotch out the corner studding, you can rip down a block,( taking off 3/4"), and fasten it as a nailer on the corner stud and run the 1x to it.

Back in the good ol' days, we always blocked out for not only cabinetry, but for other things such as towel bars, toilet roll holders, curtain blocks, anywhere you needed extra backing for not only convienence , but for custom locations of certain items. Just made life a little easier for the installers. These days you have some pretty awesome wall anchors that weren't around back in the day.

Blocking for cabinets is an unnecessary time and materials expense. The only areas that I would add blocking to would be bath areas where retrofitting it would be difficult for handicap support bars.

IIRC,
one time the homeowner insisted we install continuous 3/4" plywood behind the kitchen drywall, in strips, so that there would be fastening available everywhere. The cabinets went in really fast, no measuring needed. And you could attach anything, like a pot rack, at any point without wall anchors or molly's.
"It's just crazy enough to work"
Casey

On glass front panel uppers, blocking allows you to space the fasteners equally, a detail some folks might appreciate!