Denny (https://bostonlegal.fandom.com/wiki/Denny_Crane) is significantly more impaired in The Practice, seeming to genuinely be confused when Alan Shore (https://bostonlegal.fandom.com/wiki/Alan_Shore) calls him "Dad" - in Boston Legal, Denny seems slightly confused from time to time, but mostly uses his impairment to do whatever he likes.

Anthony Heald played Judge Cooper (http://bostonlegal.wikifoundry.com/page/Harvey+Cooper) in The Practice - a California judge who over-enunciates the word "Massachusetts" to mock the lawyers from Boston; in Boston Legal he's a Massachusetts judge of the same name, with the same quirk - for no apparent reason.

Catherine Piper (https://bostonlegal.fandom.com/wiki/Catherine_Piper) (played by Betty White) was a neighbor of Alan Shore when he was a child - in The Practice they loathe each other, and she perjures herself to screw over Alan's client out of spite - but in Boston Legal she gladly comes to Alan for help, and he gladly gives it, with no sign of past hatred.

In The Practice, Alan has a woman lawyer friend who is mentally ill but very competent. She's played by Sharon Stone, and thinks that God talks directly to her. In Boston Legal, Alan also has a woman lawyer friend with mental problems - but she's played by a different actress with different symptoms.