Forum OpenACS Q&A: Re: Ran out of database pools (pool2 pool3 pool1)
This doesn't making nesting them a good idea, but it doesn't make nesting them particularly dangerous either. Just not the right way to write queries to display data.
All db_* API procs grab handles automatically, and there are many cases where it makes perfectly good sense to do so. Shipping OpenACS defaulted to one pool would break a large amount of perfectly well-behaved code.