Well, it’s a remnant of “the old days” of Dealing Desks; but it can be seen
as a way of limiting “congestion” on the servers, although that’s a weak
excuse these days. I would not use any broker which did not allow for
order component placements anywhere. Nor cases where a Buy Limit
is converted to a different order type, such as Buy Stop due to its nearness to
the market. Unacceptable, these days…
I actually specialize in “micro scalping” so unrestricted placements of orders,
such as inside the Bid/Ask spread, for example, is something I rely upon.