The primary problem with domes is they are a crutch at best and that crutch isn't used correctly by the growers. As a result they cause more problems then they solve.

Part of this is the misleading advertising pics that show dome-covered plants which is never done, But they want to sell you domes. Part of it is because many start with overtly wet potting mix - too wet to begin with and it only gets worse. There is a world of difference between sufficiently moist for germination and overly wet and that line is difficult to recognize if one thinks that water is the plants friend. ;-) Water in any visible form is not a friend to seedlings.

Part of it is not understanding that air circulation is still needed too (vented vs. non vented domes) so they don't provide it by propping up unvented domes or draining off the excess moisture. Part of it is failure to monitor the seeds closely or frequently enough. A couple hours can make a world of difference once the process starts.

Part of it is the mistaken belief that misting is effective (it isn't) or the best way to water rather than bottom watering that allows the soil mix to control the amount of water it needs if any. Part of it is that too many try to start different seeds with very different germination rates under the same dome so some rot and die while waiting for the rest to sprout. Damp-off and root rot and rotted seeds are sure to follow.

Domes are for germination only and once there is the first sign of sprouting (not leaves, just sprouted seeds breaking the soil surface) they need to be removed or at least any that have sprouted must be removed immediately.

Experienced growers seldom use them and if they do they do it very carefully and professionals never do.

Dave

Thanks, that answers all my questions!