You don't need it. You can have the contractor install the baseboards first (obviously) and then look at it and see what you think. With some flooring and trim colors, you might see a dark line (a shadow) that bothers you, esp where there are the inevitable gaps. I have dark floors and the shadows didn't bother me, so I decided no shoe mold. Really, who's going to be inspecting your baseboards anyway? Shoe mold in a new build is for aesthetic purposes only, and a personal preference.

Agreeing with emily on many accounts
But baseboards are usually attached to the wall. So the gap between the floor and bottom of baseboard can vary depending on time of year. Solution : Attach the shoe moulding to the floor so it floats up/down with the floor

IMO, shoe molding is for amateurs. As @Interior Affairs stated, install the flooring first.

@River, shoe moulding may be needed in old construction. For example, my parents house has settled. So now the floor vs the baseboard equals large gap. A shoe moulding made sense (logistically and economically)

Our flooring people removed all our baseboards when we replaced our tile with hardwood and installed new. But then, maybe hubby wanted that to happen.

I must admit, the new baseboards look nicer than the old!

@Curt D'Onofrio-The poster said "new construction, open concept". What kind of gaps are you talking, here? Pencil sized?
There really is no excuse for putting down the base trim and then running flooring in a new build. I would remove base in an existing house if it were feasible. I'll give you an exception for dire situations.

River, in my parents home (old construction, built before 1940) the gap was like 1/8" in certain places and 1/16" gap in other places. Uneven floor. Big heavy baseboard. So, the easy way out was a shoe molding

River & Curt...
You both make good points.
IMHO, base shoe is something that should be considered on a case by case basis.
By all means, baseboard should be installed après floor installation (if at all possible).
However, depending on just how irregular the subfloor or slab is, base shoe may be the lesser of two evils in getting a nice "finished" look at the elevations, rather than "caulking" or scribing a high profile base which won't bend enough to conform.

If it's GOT to be used, however, my preference is to keep it as small as possible and discreet/subtle. Ours is 1/2" x 5/8"... and painted on painted base, please.
I can't believe some of the monstrous 3/4" QUARTER ROUND some folks resort to.
Looks like someone laid a broom handle against the wall.

HI -- No you do not need the added 1/4 round shoe molding , people are doing this less now . They just end up being a dust collector . If big gaps are there after the baseboards are on , then you will probably need them. If the hardwood has been installed properly , then you should not need the shoe mold . A thicker baseboard could be used to cover any gaps in the flooring .

I noticed some commentators have stated shoe molding is not needed "if the hardwood has been installed properly". Some may misread this and think shoe mold is used only when the flooring has not been installed properly. Shoe molding is needed in situations when the subfloor/slab is uneven. The undulations in the floor's surface will cause gaps to appear between the baseboard and the flooring material. Shoe molding conforms to the floor's surface and hides those gaps. Some of our customers prefer the look of shoe molding, as it complements tall baseboards.

Can you tell me what profile this shoe is Strataline, Inc? I would like to use this with my hardwood flooring being installed. Thank you.

If your having a hard time locating a profile it may be because most distributors and professionals call it ”shue” moulding.

I think shoe mouldings add to the baseboard and is more architecturally correct. I have a Georgian style home and I am adding shoe mouldings to the baseboards I am re doing. I have 5 and a half and plan to go 7 inches. Old ones too short. I also have some gaps and prefer not to use caulking as many do.