Well, at first I thought, cloth and steel (cabled for strength?) roof, how lame. But after thinking about it, it makes reasonable sense.
1) Much cheaper than a real roof.
2) Because it's cheaper, the stadium gets a much larger opening.
Before, the opening was just on the end and only opened a very small amount. Now, the opening is much larger and is right over the middle. Much better.
3) The roof won't be closed that often. It will probably only be closed for preseason and early in the year games. So that's 2 preseason and maybe 3 regular season games.
The roof may only be closed for rain during an event, or for summer events. For a boat show in the spring, you would want it open. For a monster truck or motorcycle event, you would want it open if possible. Most night events would want it open.
4) When the new roof is closed, it will probably be semi-transparent and let some light in. This effect may be pretty cool.
Overall, since the roof won't be closed very much, in the end, it was a very good money saving choice as it won't be used much.