depends on what is in the center of the bed..If you are doing a food forest or edible forest type of bed, then if the center is a fruit tree or shrub, then you don't have to do a lot where the trunk is..and if you are putting perennials in the bed they won't require as much attention ..esp once they are established..
I have some 8' circles with a fruit tree in the center, yeah it is difficult to reach the center but really I dont' have to much. The center is mostly planted with oregano, thyme, french tarragon, comfrey, chives and walking onions..I do have to pull some weeds but as long as the mulch is kept replenished (which I admit I'm very bad at keeping that done as I have very little mulching material avail and truck is dead)..then there aren't very many weeds.
some of my beds are also half filled with Jerusalem Artichokes, which don't even require weeding, so they are self sufficient, the areas beside them are used for annuals and fruit
trees.
one of my beds is quite wide and it is mostly asparagus under dwarf fruit trees, it also contains rhubarb, bearded iris, onions, and a few annual vegetables..sometimes it is a tad difficult to reach the weeds but if I step on a board between the asparagus plants generally I don't do much damage.
some of my borders are probably 20 ' wide, and I do admit I have to walk into those a couple times a year..carefully