About wordpress database

[Italianseolover]

Hi Guys,

During the time I have installed wordpress many times on differents folder of my hosting service for making some experiment. how can I make sure this has not slowed down and dirty my database? 
Because I'm afraid to have deleted the wordpress folders in the pasts instead of uninstall wordpress from the wordpress autoinstall panel Could old wordpress database (that I don't use any more) slow down my primary wordpress installation?

Sorry for my bad english and thank u... I am a little ignorant about databases and I am afraid about put hand on them.

[godreamvacations]

If you have old wordpress databases sitting around, it would only be a problem if you still have the WP that's connected to them still around also. If so, anyone (or a bot) that visits the old installs would be pulling data from the DB and thus draining a small fraction of resources away from your current install of WP. This shouldn't be a problem, considering you mentioned they are experimental and I assume are not in production. The more pull on the database, the more bogged down your server could become at a given time; usually not an issue unless you get sudden spikes of traffic on your experimental WP installs; which would slow production WP down. Hope that made sense.