paths too many points

Pathfinder have specific option in his panel menu. See below. Y..but I want to suggest Shape Builder tool

Specify Pathfinder options

Set Pathfinder Options from the Pathfinder panel menu or by double-clicking a Pathfinder effect in the Appearance panel.

Precision

Affects how precisely the Pathfinder effects calculate an object’s path. The more precise the calculation, the more accurate the drawing and the more time is required to generate the resulting path.

Remove Redundant Points

Removes unnecessary points as you click a Pathfinder button.

Divide And Outline Will Remove Unpainted Artwork

Deletes any unfilled objects in the selected artwork as you click the Divide or Outline button.

Mischa,

How about Rectangular Grid (Tool in the Toolbox) with 9 dividers both ways and 10 times the size of a single square?

Or, if you wish individual lines throughout, how about using the Line (Segment) Tool (or the Pen Tool if you must) for the first line, then move 10 copies, then rotate all by 90 degrees?

That's indeed how the Pathfinder operations work, they often leave remainders of the originating anchor points, even if these points are technically not necessary because of the completely straight line they're part of. (Some users prefer them to work that way...)

But there are many quick ways to get rid of these extraneous anchor points.

You could select the whole path and use the Pen tool to delete them (the minus sign will appear next to the Pen cursor).

Or you could select them all, hit backspace, and Cmd/Ctrl-J to immediately close the gap again with a line.

The menu Object > Path > Delete Anchorpoints does the same but lacks a shortcut key – you could assign a key to it, if you need to do this more often. (Know how to do this ?)

The menu Object > Path > Simplify unfortunately doesn't perform well on this.

Strange, because it should be the most obvious feature to understand this situation and its expected result.

And rubbing and rolling that funny Smooth tool (a variety of the Pencil) yields even more creases and curves, so don't go there...

Hope this helps in improving your routine.

Are you sure your squares are point to point aligned?

Maybe try to Unite tchem before?

You can try to use Shape Builder Tool or Pathfinder Unite command

Please show.