Scrolling Levels and Time Pressure
A lot of classic 2D platform games use scrolling levels, but I rarely hear anyone talk about 'why'. Scrolling levels take time to implement, can be easy to pace incorrectly, and don't make a lot of sense from a logical standpoint (Why is the player moving? What crushes the player between the edge of the screen and a tile?). If these downsides were the only things scrolling levels brought to a game, then no experienced developer would use them, and justifiably so.
So why use a scrolling level? For time pressure: the ability to force a player to complete a challenge in a certain amount of time without an explicit timer involved. Lots of games, such as Portal, use time-pressure mechanics to add challenge to their game. Let's take a look at how Phantom Block uses a scrolling level for time pressure. This level is called Flip Every Switch, and the concept behind the level should be immediately obvious.
Boomer has to flip every 
Colored Lever in the level, or the ending flag will be blocked off. To do that, he is given most of the blocks in the game: 
Ghost Blocks, 
Spring Blocks, 
Gum Blocks, 
Speed Blocks, 
Magnet Blocks, and 
Rotate Blocks.
I wanted to create a level that tested the player on each mechanic individually in a short time span. None of these block applications are particularly difficult; this level serves to reinforce old concepts. The player understands all the blocks if they can clear this level, so the placement of this level would make sense as a choke-point after everything has been introduced in previous levels.
Because the time pressure and basic validation of the player's skills is the point of this level, I tried not to make the blocks interact too much here. Switching blocks can be cumbersome in high stress situations, so I didn't want to frustrate the player too much - this level moves too fast for abstract puzzle-solving thought. To that end, there is only one time when you must switch blocks, and it is to use the Speed and Spring Blocks together to launch the 
Ballum across the gap, which is a puzzle previously introduced.
To keep the pace of the level going, I placed a lot of 
Coins around the level off the necessary path. If the player is skilled enough, they can take detours to get all of the coins while waiting for the level to scroll, giving them something to do. Struggling players don't have to deal with the coins, so the level gives them more time to complete objectives.
Hopefully by now you see the value of scrolling levels, after reading from the perspective of a developer. So the next time you see one in a platformer, don't get mad on principle! Try and see why the level is scrolling. It might be for a deeper reason than to frustrate you.
And if you do get frustrated in Phantom Block, well, you could always activate the Scroll Lock cheat.
Thanks for reading, Michael
