Thats a good question and thanks for posting it on QandA platform
So omitting the 'BorderThickness' and 'BorderBrush' properties in a WPF control style, such as a Button, can have impacts on performance. removing these properties might not significantly affect memory usage, but it can influence the visual rendering of the control.
In scenarios where the control is used extensively, like in lists or treeviews, like you mentioned simplifying the visual appearance by excluding unnecessary borders could potentially improve rendering speed
So answering to the entire question omitting these properties might have a slight positive impact on performance, it's crucial to balance visual appearance with efficiency.
If this helps kindly accept the answer thanks much.