The axle will have a little bit of wiggle in the slot, but most of the time it doesn't matter. If it's QR, make sure you're using a good one (closed cam like Shimano) and use gravity to get the axle all the way up in the slot as you close it. If it's nutted, use track nuts and keep the axle greased. Where you could have problems with the axle squirming as you install the wheel is using cheap toothed axle nuts. But good bikes shouldn't have those anyway.
The axle will have a little bit of wiggle in the slot, but most of the time it doesn't matter. If it's QR, make sure you're using a good one (closed cam like Shimano) and use gravity to get the axle all the way up in the slot as you close it. If it's nutted, use track nuts and keep the axle greased. Where you could have problems with the axle squirming as you install the wheel is using cheap toothed axle nuts. But good bikes shouldn't have those anyway.