I wear mostly UK Mockers. While Mockers have nice deep front pockets, I don't like heavy or bulky items (my phone, keys, pens, etc...) in my front pockets and really hate anything in my back pockets (whether kilted or not.) I have two 'original' UKs with the big pockets, but they don't get a lot of wear. A sporran looks just fine with a Mocker.

As mentioned earlier in this thread, the sporran also helps keep the aprons in check as well (if not better) than a modesty snap and it reiterates and reinforces that you are not cross dressing in public. Not that there is anything wrong with cross dressing in public, if it is your thing, but it isn't everyone's thing.