We had more than 3m extra records on a site and the db snowballed to 1.3gb ( that was just the options table) after cleaning we got down to a few mb and are able to more easily work on the site.
It is more stable. After running the transients clean step I also optimised the tables as there was still overhead left in the db so it is a 2 step process ( especially for the larger tables.)
Thanks again. While I ended up running the sql query directly this is easier in a maintenance situation.