I did this more or less as an experiment

The idea of preferring slow speeds is that you contribute to with a small % (say 1%) to each block
worded by your mining pool. If your MiningPool wins that block, you get your 1% of the reward associated
with that block. Otherwise my computational power is lost.
So, if your mining Pool wins say 10blocks/day, after 1 day of work statistically you get (10*Reward_of_each_block)* (1%).
The problem, instead, of renting a lot of computational power for a short time is that I might
contribute 50% just for a couple of blocks, and if those blocks don't win, I'm screwed.
(If the win, instead, I can get much more reward).
Is what I wrote above correct? Sorry I'm a total noob with mining!

Another specific question: what are the 'Round Shares' ? Are they collected over multiple blocks, or reset to zero after each block (won or lost)?
That's the idea; if you flip a coin long enough then it will be 50% heads.
It's PPLNS so the shares are a bit confusing; you will get shares even after you have stopped mining and is not equal throughout the round.
Pool is using PPLNS. So you get less at starting blocks but get more from last blocks. You even get few round of rewards even when you stop mining.