Does voting power below 100% affect something and isnt good for account?
It just affects your upvote value. The less voting power you have - the less is your upvote value in $ next to the post what you have upvoted. Nothing more and nothing less.

BUT: In my opinion the upvote value is not as important as the vote itself or comments. Interaction with the creator is the most important - not the ammount of money we "send" him. Of course it is good to give 0.1$ instead of 0.01$ but yeah for me as creator the upvote itself counts much more.
It would obviously go below 100% if you vote someone, and having it 100 % all the time ( mean you are not voting anything) does not make any sense, because that means you are not voting anyone, but you expect votes from others, which portrays you as selfish. Comments are one way of engagement, but a comment with a vote is certainly the ideal way to show your love to others and build engagement with the community.

So have it over 85 - 90 percentage so that it gets recharged every day, and your vote has some value. Hope that answers.
Yes it does effect you vote weight and value of you upvote. However as you share you vote you help to increase reward pool for all steeemians and help other people and yourself grow via curation.

When you don't use your vote you are sitting on idle power that is not doing anything for anyone. You want to manage you vote by casting more votes with less vote % applied to the weight and cast more votes than not using it at all.

A few platforms and plugins allow you to do this by doing this you are casting more vote and helping more people without sitting on idle power.
It only affects how much vote value and curation rewards you will get back when the post hits payout. Generally speaking you want to keep it as close as possible to 100
POWER below 80% gets bad. You have to keep your power in 80% and 99% to make money of curation rewards.
Your upvote is getting lower when your voting power is going down