I've found that compiler divides my map using this (obvious), but it don't cut map at coords using this setting (i.e. at 0, 1024, 2048, etc) but at some coords which looks random to me and they change sometimes (even after I do some minor changes in my map). Is there any way to control 'cutting' points ? What is your advice about value.
My map has some open areas, like long street with high buildings, etc.

maxnodesize is the max limit for VIS leafnodes that BSP makes. and no wpoly can be in more than one leafnode, so that is another cut line for wpolys, as you noticed.

1024 is the maxnodesize default. IF you map has a lot of wide open areas and IF you stretched textures more than 4x, ONLY then is it worth increasing maxnodesize to 2048.

it you didn't stretch textures that much, then the maxnodesize is not cutting up wpolys as much as the wpoly subdivide is, so you will not get much benifit from changing it. feel free to try a compile with hlbsp -maxnodesize 2048 and see if there is any real improvement in r_speeds, i doubt much. you may even get WORSE r_speeds in places because big leafnodes contain more wpoly brushes.....

also if you have lots of small corridors, you may find that LOWERING maxnodesize to 512 will help your r_speeds more - the leafnodes will not be as long, so VIS will be more broken up around corners.

but playing with maxnodesize for r_speeds will only tweek things a teeny little, whether you go up to 2048 or down to 512. and you should save it for you next to final compile when your map is almost done.

I understand this. But exact cut plane isn't positioned in any clear way and it moves after some map changes. So when I optimize some brushes and continue working on map, after some time compiler places cut plane in different place and prev. optimizations are 'destroyed'. It is very annoying cause I have nice long street with buildings and windows. I don't want to close too much of them to reduce r_speeds (it tops about 1000 here), but I want to reduce unnecessary cuts compiler makes.

edit:
Maybe using larger value (like 2048 or more) + manual hinting will give better results ?

well, every time you change a map you have a chance the compilers will reorder the leafnodes into new shapes & sizes.

HINT brushes can help some, but they are not a guarantee and come with some cutting problems of their own.

it is really best to pretty much finish the map with good principles, and then at the end start playing with HINTs and maxleafnode sizing. otherwise you are making work for yourself at every stage.