You always need a filler against a wall with full overlay cabinets because walls are not straight and true. I usually split a 3" filler into 1 1/2" because that's fairly easy for the installer, but in instances where every inch counted, I've used a 1" filler. If you place a pull out next to a wall without a filler, you run the risk of scraping the wall every single time you use it where there is a high spot in that wall. Also, this cannot be a "filler pullout" cabinet as those have to go between two cabinets, not next to walls or appliances. At least it can't go next to a wall without blocking and panels that your installer will charge you extra and cuss you for. It can be a "pantry pull out" with a filler next to it against the wall.

Does the adjacent wall also have a doorway closer than the full extension of the pull out? If so, you need to be far enough away to clear any door trim.

We are using frameless, which are by definition full overlay, cabinets to squeeze every inch out of our small kitchen. But we still have filler. I think it's 1 inch next to each wall where we have cabinets. We have a spice pull out, a tray pull out, a drawer stack, and a pantry pull out next to walls, so a very small spacer at each place for the reasons above. We also have a spacer by the fridge in our upper cabinets since it sticks out past the length of the door, so to allow space for the handle when opened all the way there's a spacer. That one is actually like 2.5 inches to make the cabinets look balanced around the window. If I didn't have a fridge end panel I would have had enough room for a 3 inch size increase, but missing fractions of an inch are the story of my kitchen.

I've read that in fully custom builds the spacer can be made as part of the cabinet, with the door positioned accordingly. But I bet that's $$$$$$.

Good information - I can deal with a 1" filler.