Always open at windows at 50%

[mckcd]

Is this possible. I use a large screen, I would like side by side when I have two open.

[Thesola10]

You can use the Winprops feature to achieve this, add a rule with /.*/ in wmclass and preferred width to 50% to have every window open at 50% screen width by default.

It sounds like your use case would be better served by a traditional tiling WM though.